© 2015 Pearson Education, Inc.

Cell Division and Reproduction
© 2015 Pearson Education, Inc.

8.1 Cell division plays many important roles in the lives of organisms
The ability of organisms to reproduce their own kind is a key characteristic of life. Student Misconceptions and Concerns • As the textbook authors note in Module 8.1, biologists use the term “daughter” to indicate offspring and not gender. Students with little experience in this terminology can easily become confused. • Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for these topics in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated by government. Teaching Tips • Sometimes the most basic questions can challenge students and get them focused on the subject at hand. Consider asking your students why we expect that dogs will produce dogs, cats will produce more cats, and chickens will only produce chickens. Why does like produce like? © 2015 Pearson Education, Inc.

is reproduction at the cellular level, produces two “daughter” cells that are genetically identical to each other and the original “parent” cell, requires the duplication of chromosomes, the structures that contain most of the cell’s DNA, and sorts new sets of chromosomes into the resulting pair of daughter cells. Student Misconceptions and Concerns • As the textbook authors note in Module 8.1, biologists use the term “daughter” to indicate offspring and not gender. Students with little experience in this terminology can easily become confused. • Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for these topics in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated by government. Teaching Tips • Sometimes the most basic questions can challenge students and get them focused on the subject at hand. Consider asking your students why we expect that dogs will produce dogs, cats will produce more cats, and chickens will only produce chickens. Why does like produce like? © 2015 Pearson Education, Inc.

Living organisms reproduce by two methods. Asexual reproduction produces offspring that are identical to the original cell or organism and involves inheritance of all genes from one parent. Sexual reproduction produces offspring that are similar to the parents but show variations in traits and involves inheritance of unique sets of genes from two parents. Student Misconceptions and Concerns • As the textbook authors note in Module 8.1, biologists use the term “daughter” to indicate offspring and not gender. Students with little experience in this terminology can easily become confused. • Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for these topics in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated by government. Teaching Tips • Sometimes the most basic questions can challenge students and get them focused on the subject at hand. Consider asking your students why we expect that dogs will produce dogs, cats will produce more cats, and chickens will only produce chickens. Why does like produce like? © 2015 Pearson Education, Inc.

Cell division is used for reproduction of single-celled organisms, growth of multicellular organisms from a fertilized egg into an adult, repair and replacement of cells, and production of sperm and eggs. Student Misconceptions and Concerns • As the textbook authors note in Module 8.1, biologists use the term “daughter” to indicate offspring and not gender. Students with little experience in this terminology can easily become confused. • Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for these topics in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated by government. Teaching Tips • Sometimes the most basic questions can challenge students and get them focused on the subject at hand. Consider asking your students why we expect that dogs will produce dogs, cats will produce more cats, and chickens will only produce chickens. Why does like produce like? © 2015 Pearson Education, Inc.

Figure 8.1a Figure 8.1a A yeast cell producing a genetically identical daughter cell by asexual reproduction

Figure 8.1f Figure 8.1f A human kidney cell dividing

8.2 Prokaryotes reproduce by binary fission
Prokaryotes (single-celled bacteria and archaea) reproduce by binary fission (“dividing in half”). The chromosome of a prokaryote is typically a single circular DNA molecule associated with proteins and much smaller than those of eukaryotes. Student Misconceptions and Concerns • Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for these topics in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated by government. Teaching Tips • The principle that “every cell comes from another cell” is worth thinking through with your class. Students might expect that, like automobiles, computers, and cell phones, parts are constructed and cells are assembled. In our society, few nonliving products are generated only from existing products (try to think of such examples). For example, you do not need a painting to paint or a house to construct a house. Yet, this is a common expectation in biology. Further, students who think through this principle might ask how the first cells formed. They might wonder further whether the same environments that produced these cells are still in existence. The conditions on Earth when life first formed were very different from those we know today. Chapter 15 of the textbook addresses the origin and early evolution of life on Earth. • Consider contrasting the timing of DNA replication and cytokinesis in prokaryotes and eukaryotes. In prokaryotes, addressed in Module 8.2 of the textbook, these processes are overlapping. However, as revealed in the next few modules, these events are separate in eukaryotes. © 2015 Pearson Education, Inc.

8.2 Prokaryotes reproduce by binary fission
Binary fission of a prokaryote occurs in three stages: duplication of the chromosome and separation of the copies, continued elongation of the cell and movement of the copies, and division into two daughter cells. Student Misconceptions and Concerns • Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for these topics in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated by government. Teaching Tips • The principle that “every cell comes from another cell” is worth thinking through with your class. Students might expect that, like automobiles, computers, and cell phones, parts are constructed and cells are assembled. In our society, few nonliving products are generated only from existing products (try to think of such examples). For example, you do not need a painting to paint or a house to construct a house. Yet, this is a common expectation in biology. Further, students who think through this principle might ask how the first cells formed. They might wonder further whether the same environments that produced these cells are still in existence. The conditions on Earth when life first formed were very different from those we know today. Chapter 15 of the textbook addresses the origin and early evolution of life on Earth. • Consider contrasting the timing of DNA replication and cytokinesis in prokaryotes and eukaryotes. In prokaryotes, addressed in Module 8.2 of the textbook, these processes are overlapping. However, as revealed in the next few modules, these events are separate in eukaryotes. © 2015 Pearson Education, Inc.

Prokaryotic chromosome
Figure 8.2a-3 Plasma membrane Prokaryotic chromosome Cell wall Duplication of the chromosome and separation of the copies 1 Continued elongation of the cell and movement of the copies 2 Figure 8.2a-3 Binary fission of a prokaryotic cell (step 3) Division into two daughter cells 3

Prokaryotic chromosomes
Figure 8.2b Prokaryotic chromosomes Figure 8.2b An electron micrograph of a dividing bacterium

The Eukaryotic Cell Cycle and Mitosis

8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division
Eukaryotic cells are more complex and larger than prokaryotic cells, have more genes, and store most of their genes on multiple chromosomes within the nucleus. Each eukaryotic species has a characteristic number of chromosomes in each cell nucleus. Student Misconceptions and Concerns • Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic when discussing DNA replication. • Students are often confused by photographs of chromosomes. Such photographs, such as Figure 8.3B, typically show duplicated chromosomes during some aspect of cell division. It remains unclear to many (a) why chromosome structure is typically different between interphase G1 and the stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes duplicate. Teaching Tips • Figure 8.3B is an important point of reference for some basic terminology. Consider referring to it as you distinguish between a DNA molecule and a chromosome, unreplicated and replicated chromosomes, and the nature of sister chromatids. • Consider an analogy between the precise packaging of DNA into chromosomes and packing a home for a move to another home. Tap into the intuitive advantages of packaging DNA using this or any other analogy of highly packaged materials (perhaps a boxed “desk” that requires some assembly). • The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids. We have doubled the DNA, but the molecules remain attached (although not attached in the same way as the wire). You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes. © 2015 Pearson Education, Inc.

Eukaryotic chromosomes are composed of chromatin consisting of one long DNA molecule and proteins that help maintain the chromosome structure and control the activity of its genes. To prepare for division, the chromatin becomes highly compact and visible with a microscope. Student Misconceptions and Concerns • Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic when discussing DNA replication. • Students are often confused by photographs of chromosomes. Such photographs, such as Figure 8.3B, typically show duplicated chromosomes during some aspect of cell division. It remains unclear to many (a) why chromosome structure is typically different between interphase G1 and the stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes duplicate. Teaching Tips • Figure 8.3B is an important point of reference for some basic terminology. Consider referring to it as you distinguish between a DNA molecule and a chromosome, unreplicated and replicated chromosomes, and the nature of sister chromatids. • Consider an analogy between the precise packaging of DNA into chromosomes and packing a home for a move to another home. Tap into the intuitive advantages of packaging DNA using this or any other analogy of highly packaged materials (perhaps a boxed “desk” that requires some assembly). • The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids. We have doubled the DNA, but the molecules remain attached (although not attached in the same way as the wire). You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes. © 2015 Pearson Education, Inc.

Figure 8.3a Figure 8.3a A plant cell (from an African blood lily) just before cell division

Chromosomal DNA molecules
Figure 8.3b-0 Chromosomes Chromosomal DNA molecules Sister chromatids Chromosome duplication Sister chromatids Centromere Figure 8.3b-0 Chromosome duplication and distribution Separation of sister chromatids and distribution into two daughter cells

Before a eukaryotic cell begins to divide, it duplicates all of its chromosomes, resulting in two copies called sister chromatids. The sister chromatids are joined together along their lengths and are cinched especially tightly at a narrowed “waist” called the centromere. When a cell divides, the sister chromatids separate from each other and are then called chromosomes, and sort into separate daughter cells. Student Misconceptions and Concerns • Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic when discussing DNA replication. • Students are often confused by photographs of chromosomes. Such photographs, such as Figure 8.3B, typically show duplicated chromosomes during some aspect of cell division. It remains unclear to many (a) why chromosome structure is typically different between interphase G1 and the stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes duplicate. Teaching Tips • Figure 8.3B is an important point of reference for some basic terminology. Consider referring to it as you distinguish between a DNA molecule and a chromosome, unreplicated and replicated chromosomes, and the nature of sister chromatids. • Consider an analogy between the precise packaging of DNA into chromosomes and packing a home for a move to another home. Tap into the intuitive advantages of packaging DNA using this or any other analogy of highly packaged materials (perhaps a boxed “desk” that requires some assembly). • The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids. We have doubled the DNA, but the molecules remain attached (although not attached in the same way as the wire). You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes. © 2015 Pearson Education, Inc.

8.4 The cell cycle includes growing and division phases
The cell cycle is an ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division. Teaching Tips • The textbook authors note in Module 8.4 that each of your students consists of about 10 trillion cells. It is likely that this number is beyond comprehension for most of your students. Consider sharing several simple examples of the enormity of that number to try to make it more meaningful. For example, the U.S. population in 2014 is about 317 million people. To give every one of those people about $31,500, we will need a total of 10 trillion dollars. Here is another example. If we gave you $32,000 every second, it would take 10 years to give you 10 trillion dollars. The U.S. Debt Clock helps relate these large numbers to the U.S. national debt at • In G1, the chromosomes have not duplicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle. © 2015 Pearson Education, Inc.

8.4 The cell cycle includes growing and division phases
The cell cycle consists of two stages, characterized as follows: Interphase: duplication of cell contents G1—growth, increase in cytoplasm S—duplication of chromosomes G2—growth, preparation for division Mitotic phase: division Mitosis—division of the nucleus Cytokinesis—division of cytoplasm Teaching Tips • The textbook authors note in Module 8.4 that each of your students consists of about 10 trillion cells. It is likely that this number is beyond comprehension for most of your students. Consider sharing several simple examples of the enormity of that number to try to make it more meaningful. For example, the U.S. population in 2014 is about 317 million people. To give every one of those people about $31,500, we will need a total of 10 trillion dollars. Here is another example. If we gave you $32,000 every second, it would take 10 years to give you 10 trillion dollars. The U.S. Debt Clock helps relate these large numbers to the U.S. national debt at • In G1, the chromosomes have not duplicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle. © 2015 Pearson Education, Inc.

G1 (first gap) S (DNA synthesis) M G2 (second gap)
Figure 8.4 G1 (first gap) S (DNA synthesis) M Cytokinesis G2 (second gap) Mitosis Figure 8.4 The eukaryotic cell cycle

8.5 Cell division is a continuum of dynamic changes
Mitosis progresses through a series of stages: prophase, prometaphase, metaphase, anaphase, and telophase. Cytokinesis often overlaps telophase. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

A mitotic spindle is required to divide the chromosomes, guides the separation of the two sets of daughter chromosomes, and is composed of microtubules and associated proteins. Spindle microtubules emerge from two centrosomes, microtubule-organizing regions in the cytoplasm of eukaryotic cells. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Interphase Prophase Prometaphase Fragments of the nuclear envelope
Figure 8.5-2 Interphase Prophase Prometaphase Fragments of the nuclear envelope Centrosomes Early mitotic spindle Chromatin Centrosome Kinetochore Figure The stages of cell division by mitosis: interphase through prometaphase Centromere Nuclear envelope Plasma membrane Spindle microtubules Chromosome, consisting of two sister chromatids

Interphase The cytoplasmic contents double. Two centrosomes form. Chromosomes duplicate in the nucleus during the S phase. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Mitosis Interphase Prophase Prometaphase
Figure 8.5-1 Mitosis Interphase Prophase Prometaphase Centrosomes Fragments of the nuclear envelope Early mitotic spindle Chromatin Centrosome Kinetochore Figure The stages of cell division by mitosis: interphase through prometaphase Centromere Nuclear envelope Spindle microtubules Plasma membrane Chromosome, consisting of two sister chromatids

Prophase In the nucleus, chromosomes become more tightly coiled and folded. In the cytoplasm, the mitotic spindle begins to form as microtubules rapidly grow out from the centrosomes. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Prometaphase The nuclear envelope breaks into fragments and disappears. Microtubules extend from the centrosomes into the nuclear region. Some spindle microtubules attach to the kinetochores. Other microtubules meet those from the opposite poles. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Telophase and Cytokinesis
Figure 8.5-7 Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Nuclear envelope forming Figure The stages of cell division by mitosis: metaphase through cytokinesis Separated chromosomes Mitotic spindle

Mitosis Metaphase Anaphase Telophase and Cytokinesis Metaphase plate
Figure 8.5-6 Mitosis Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Figure The stages of cell division by mitosis: metaphase through cytokinesis Nuclear envelope forming Separated chromosomes Mitotic spindle

Metaphase The mitotic spindle is fully formed. Chromosomes align at the cell equator. Kinetochores of sister chromatids are facing the opposite poles of the spindle. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Anaphase Sister chromatids separate at the centromeres. Daughter chromosomes are moved to opposite poles of the cell as motor proteins move the chromosomes along the spindle microtubules and kinetochore microtubules shorten. Spindle microtubules not attached to chromosomes lengthen, moving the poles farther apart. At the end of anaphase, the two ends of the cell have equal collections of chromosomes. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Telophase The cell continues to elongate. The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei. Chromatin uncoils. The mitotic spindle disappears. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

During cytokinesis, the cytoplasm is divided into separate cells. Cytokinesis usually occurs simultaneously with telophase. Teaching Tips • Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT, which are the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

8.6 Cytokinesis differs for plant and animal cells
In animal cells, cytokinesis occurs as a cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin, and the cleavage furrow deepens to separate the contents into two cells. Teaching Tips • Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). This occurs in human development during the formation of the placenta. • The authors make an analogy between a drawstring on a hooded sweatshirt and the mechanism of cytokinesis in animal cells. Students seem to appreciate this association. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because, like the drawstring just beneath the surface of the sweatpants, the microfilaments are just beneath the surface of the cell’s plasma membrane. © 2015 Pearson Education, Inc.

Contracting ring of microfilaments
Figure 8.6a-0 Cytokinesis Cleavage furrow Contracting ring of microfilaments Figure 8.6a-0 Cleavage of an animal cell Daughter cells

8.6 Cytokinesis differs for plant and animal cells
In plant cells, cytokinesis occurs as a cell plate forms in the middle, from vesicles containing cell wall material, the cell plate grows outward to reach the edges, dividing the contents into two cells, and each cell now possesses a plasma membrane and cell wall. Teaching Tips • Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). This occurs in human development during the formation of the placenta. • The authors make an analogy between a drawstring on a hooded sweatshirt and the mechanism of cytokinesis in animal cells. Students seem to appreciate this association. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because, like the drawstring just beneath the surface of the sweatpants, the microfilaments are just beneath the surface of the cell’s plasma membrane. © 2015 Pearson Education, Inc.

Cell wall of the parent cell Cell wall
Figure 8.6b-0 Cytokinesis New cell wall Cell wall of the parent cell Cell wall Daughter nucleus Cell plate forming Figure 8.6b-0 Cell plate formation in a plant cell Vesicles containing cell wall material Cell plate Daughter cells

8.7 Anchorage, cell density, and chemical growth factors affect cell division
The cells within an organism’s body divide and develop at different rates. Cell division is controlled by anchorage dependence, the need for cells to be in contact with a solid surface to divide, density-dependent inhibition, in which crowded cells stop dividing, the presence of essential nutrients, and growth factors, proteins that stimulate division. Teaching Tips • Students who closely examine a small abrasion on their skin might notice that the wound tends to heal from the outer edges inward. This space-filling mechanism is a natural example of density-dependent density-dependent inhibition, which is also seen when cells in a cell culture dish stop dividing when they have formed a complete layer. © 2015 Pearson Education, Inc.

Restoration of single layer by cell division
Figure 8.7a Anchorage Single layer of cells Removal of cells Figure 8.7a An experiment demonstrating density-dependent inhibition, using animal cells grown in culture Restoration of single layer by cell division Cancer cells forming clump of overlapping cells

Cultured cells suspended in liquid
Figure 8.7b Cultured cells suspended in liquid The addition of growth factor Figure 8.7b An experiment demonstrating the effect of growth factors on the division of cultured animal cells Cells divide in presence of growth factor Cells fail to divide

8.8 Growth factors signal the cell cycle control system
The cell cycle control system is a cycling set of molecules in the cell that triggers and coordinates key events in the cell cycle. Checkpoints in the cell cycle can stop an event or signal an event to proceed. Teaching Tips • The cell cycle control system depicted in Figure 8.8A is like the control device of an automatic washing machine (which uses a turning dial). Each has a control system that triggers and coordinates key events in the cycle. However, unlike a washing machine, the components of the control system of a cell cycle are not all located in one place. © 2015 Pearson Education, Inc.

8.8 Growth factors signal the cell cycle control system
There are three major checkpoints in the cell cycle. G1 checkpoint: allows entry into the S phase or causes the cell to leave the cycle, entering a nondividing G0 phase. G2 checkpoint M checkpoint Research on the control of the cell cycle is one of the hottest areas in biology today. Teaching Tips • The cell cycle control system depicted in Figure 8.8A is like the control device of an automatic washing machine (which uses a turning dial). Each has a control system that triggers and coordinates key events in the cycle. However, unlike a washing machine, the components of the control system of a cell cycle are not all located in one place. © 2015 Pearson Education, Inc.

G1 checkpoint G0 G1 S Control system M G2 M checkpoint G2 checkpoint
Figure 8.8a G1 checkpoint G0 G1 S Control system M Figure 8.8a A schematic model for the cell cycle control system G2 M checkpoint G2 checkpoint

G1 checkpoint Receptor protein
Figure 8.8b Extracellular fluid Plasma membrane Growth factor Relay proteins G1 checkpoint Receptor protein Signal transduction pathway S G1 Control system Figure 8.8b How a growth factor signals the cell cycle control system M G2 Cytoplasm

8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors
Cancer currently claims the lives of 20% of the people in the United States. Cancer cells escape controls on the cell cycle. Cancer cells divide excessively and invade other tissues of the body. Student Misconceptions and Concerns • Students do not typically know that not all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer. Teaching Tips • Chemotherapy has some disastrous side effects. The drugs used to fight cancer may attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection. Many other approaches to attack cancers are under consideration. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. Active Lecture Tips • See the Activity Losing Control of a Car Relates to Unregulated Cell Division on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

A tumor is a mass of abnormally growing cells within otherwise normal tissue. Benign tumors remain at the original site but may disrupt certain organs if they grow in size. Malignant tumors can spread to other locations in a process called metastasis. An individual with a malignant tumor is said to have cancer. Student Misconceptions and Concerns • Students do not typically know that not all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer. Teaching Tips • Chemotherapy has some disastrous side effects. The drugs used to fight cancer may attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection. Many other approaches to attack cancers are under consideration. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. Active Lecture Tips • See the Activity Losing Control of a Car Relates to Unregulated Cell Division on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

another part of the body
Figure 8.9 Lymph vessels Blood vessel Tumor Tumor in another part of the body Glandular tissue Figure 8.9 Growth and metastasis of a malignant (cancerous) tumor of the breast Tumor growth Invasion Metastasis

Cancers are named according to the organ or tissue in which they originate. Carcinomas originate in external or internal body coverings. Leukemia originates from immature white blood cells within the blood or bone marrow. Student Misconceptions and Concerns • Students do not typically know that not all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer. Teaching Tips • Chemotherapy has some disastrous side effects. The drugs used to fight cancer may attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection. Many other approaches to attack cancers are under consideration. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. Active Lecture Tips • See the Activity Losing Control of a Car Relates to Unregulated Cell Division on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Localized tumors can be removed surgically and/or treated with concentrated beams of high-energy radiation. Metastatic tumors are treated with chemotherapy. Student Misconceptions and Concerns • Students do not typically know that not all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer. Teaching Tips • Chemotherapy has some disastrous side effects. The drugs used to fight cancer may attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection. Many other approaches to attack cancers are under consideration. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. Active Lecture Tips • See the Activity Losing Control of a Car Relates to Unregulated Cell Division on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Meiosis and Crossing Over

8.11 Chromosomes are matched in homologous pairs
In humans, somatic cells have 46 chromosomes forming 23 pairs of homologous chromosomes. Student Misconceptions and Concerns • Some students might conclude that sex chromosomes function only in determining the sex of an individual. As the authors note, sex chromosomes contain genes not involved in sex determination. Teaching Tips • Students might recall some basic genetics, remembering that for many traits a person receives a separate “signal” from mom and dad. These separate signals for the same trait are carried on the same portion of homologous chromosomes, such as the freckle trait noted in Module 8.11 of the textbook. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Homologous chromosomes are matched in length, centromere position, and staining pattern. A locus (plural, loci) is the position of a gene. Different versions of a gene may be found at the same locus on the two chromosomes of a homologous pair. Student Misconceptions and Concerns • Some students might conclude that sex chromosomes function only in determining the sex of an individual. As the authors note, sex chromosomes contain genes not involved in sex determination. Teaching Tips • Students might recall some basic genetics, remembering that for many traits a person receives a separate “signal” from mom and dad. These separate signals for the same trait are carried on the same portion of homologous chromosomes, such as the freckle trait noted in Module 8.11 of the textbook. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

The human sex chromosomes X and Y differ in size and genetic composition. The other 22 pairs of chromosomes are autosomes with the same size and genetic composition. Student Misconceptions and Concerns • Some students might conclude that sex chromosomes function only in determining the sex of an individual. As the authors note, sex chromosomes contain genes not involved in sex determination. Teaching Tips • Students might recall some basic genetics, remembering that for many traits a person receives a separate “signal” from mom and dad. These separate signals for the same trait are carried on the same portion of homologous chromosomes, such as the freckle trait noted in Module 8.11 of the textbook. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Pair of homologous duplicated chromosomes One duplicated chromosome
Figure 8.11 Pair of homologous duplicated chromosomes Locus Centromere Sister chromatids Figure 8.11 A pair of homologous chromosomes One duplicated chromosome

8.12 Gametes have a single set of chromosomes
An organism’s life cycle is the sequence of stages leading from the adults of one generation to the adults of the next. Humans and many animals and plants are diploid, because all somatic cells contain pairs of homologous chromosomes. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Consider helping students think through mitosis and meiosis by developing an analogy to pairs of shoes. In this case, any given species has a certain number of pairs of shoes, or homologous chromosomes. • In the shoe analogy, females have 23 pairs of matching shoes, while males have 22 matching pairs and 1 odd pair maybe a sandal and a sneaker! • You might want to get your students thinking by asking them why eggs and sperm are different. (This depends upon the species, but within vertebrates, eggs and sperm are specialized for different tasks. Sperm are adapted to move to an egg and donate a nucleus. Eggs contain a nucleus and most of the cytoplasm of the future zygote. Thus eggs are typically larger, nonmotile, and full of cellular resources to sustain cell division and growth.) Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

are eggs and sperm and are said to be haploid because each cell has a single set of chromosomes. The human life cycle begins when a haploid sperm fuses with a haploid egg in fertilization. The zygote, formed by fertilization, is now diploid. Mitosis of the zygote and its descendants generates all the somatic cells into the adult form. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Consider helping students think through mitosis and meiosis by developing an analogy to pairs of shoes. In this case, any given species has a certain number of pairs of shoes, or homologous chromosomes. • In the shoe analogy, females have 23 pairs of matching shoes, while males have 22 matching pairs and 1 odd pair maybe a sandal and a sneaker! • You might want to get your students thinking by asking them why eggs and sperm are different. (This depends upon the species, but within vertebrates, eggs and sperm are specialized for different tasks. Sperm are adapted to move to an egg and donate a nucleus. Eggs contain a nucleus and most of the cytoplasm of the future zygote. Thus eggs are typically larger, nonmotile, and full of cellular resources to sustain cell division and growth.) Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

n n Haploid gametes (n = 23) Key n Haploid stage (n) Egg cell
Figure 8.12a Haploid gametes (n = 23) Key n n Haploid stage (n) Egg cell Diploid stage (2n) n n Sperm cell Meiosis Fertilization Ovary Testis Figure 8.12a The human life cycle 2n Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46)

Gametes are made by meiosis in the ovaries and testes. Meiosis reduces the chromosome number by half. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Consider helping students think through mitosis and meiosis by developing an analogy to pairs of shoes. In this case, any given species has a certain number of pairs of shoes, or homologous chromosomes. • In the shoe analogy, females have 23 pairs of matching shoes, while males have 22 matching pairs and 1 odd pair maybe a sandal and a sneaker! • You might want to get your students thinking by asking them why eggs and sperm are different. (This depends upon the species, but within vertebrates, eggs and sperm are specialized for different tasks. Sperm are adapted to move to an egg and donate a nucleus. Eggs contain a nucleus and most of the cytoplasm of the future zygote. Thus eggs are typically larger, nonmotile, and full of cellular resources to sustain cell division and growth.) Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Sister chromatids separate Haploid cells
Figure 8.12b Interphase Meiosis I Meiosis II Sister chromatids 1 2 3 Sister chromatids separate Haploid cells Chromosomes duplicate Homologous chromosomes separate A pair of homologous chromosomes in a diploid parent cell A pair of duplicated homologous chromosomes Figure 8.12b How meiosis halves chromosome number

8.13 Meiosis reduces the chromosome number from diploid to haploid
Meiosis is a type of cell division that produces haploid gametes in diploid organisms. Two haploid gametes may then combine in fertilization to restore the diploid state in the zygote. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Meiosis and mitosis are preceded by the duplication of chromosomes. However, meiosis is followed by two consecutive cell divisions and mitosis is followed by only one cell division. Because in meiosis, one duplication of chromosomes is followed by two divisions, each of the four daughter cells produced has a haploid set of chromosomes. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Interphase: Like mitosis, meiosis is preceded by an interphase, during which the chromosomes duplicate. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Meiosis I – Prophase I key events The nuclear membrane dissolves. Chromatin tightly coils up. Homologous chromosomes, each composed of two sister chromatids, come together in pairs in a process called synapsis. During synapsis, chromatids of homologous chromosomes exchange segments in a process called crossing over. The chromosome tetrads move toward the center of the cell. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Interphase: Chromosomes duplicate
Figure Interphase: Chromosomes duplicate Meiosis I: Homologous chromosomes separate Prophase I Metaphase I Anaphase I Sites of crossing over Spindle microtubules attached to a kinetochore Sister chromatids remain attached Centrosomes Spindle Tetrad Figure The stages of meiosis (part 1) Metaphase plate Nuclear envelope Chromatin Sister chromatids Fragments of the nuclear envelope Centromere (with a kinetochore) Homologous chromosomes separate

Interphase: Chromosomes duplicate
Figure Interphase: Chromosomes duplicate Meiosis I: Prophase I Sites of crossing over Centrosomes Spindle Figure The stages of meiosis (part 2) Tetrad Nuclear envelope Chromatin Sister chromatids Fragments of the nuclear envelope

Meiosis I – Metaphase I: Tetrads align at the cell equator. Meiosis I – Anaphase I Homologous pairs separate and move toward opposite poles of the cell. Unlike mitosis, the sister chromatids making up each doubled chromosome remain attached. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Meiosis I: Metaphase I Anaphase I
Figure Meiosis I: Metaphase I Anaphase I Spindle microtubules attached to a kinetochore Sister chromatids remain attached Figure The stages of meiosis (part 3) Metaphase plate Centromere (with a kinetochore) Homologous chromosomes separate

Meiosis I – Telophase I Duplicated chromosomes have reached the poles. Usually, cytokinesis occurs along with telophase. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Telophase I and Cytokinesis
Figure Telophase I and Cytokinesis Cleavage furrow Figure The stages of meiosis (part 5)

Meiosis II follows meiosis I without chromosome duplication. Each of the two haploid products enters meiosis II. Meiosis II – Prophase II A spindle forms and moves chromosomes toward the middle of the cell. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Meiosis II – Metaphase II: Duplicated chromosomes align at the cell equator like they are in mitosis. Meiosis II – Anaphase II Sister chromatids separate. Individual chromosomes move toward opposite poles. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Meiosis II: Sister chromatids separate
Figure Meiosis II: Sister chromatids separate Telophase I and Cytokinesis Telophase II and Cytokinesis Prophase II Metaphase II Anaphase II Cleavage furrow Sister chromatids separate Haploid daughter cells forming Figure The stages of meiosis (part 4)

Meiosis II – Telophase II Chromosomes have reached the poles of the cell. A nuclear envelope forms around each set of chromosomes. With cytokinesis, four haploid cells are produced. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • Challenge students to identify which stage of meiosis is most like mitosis. Comparing the specific events of mitosis, meiosis I, and meiosis II to each other allows students to identify essential differences. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

8.14 VISUALIZING THE CONCEPT: Mitosis and meiosis have important similarities and differences
Mitosis and meiosis both begin with diploid parent cells that have chromosomes duplicated during the previous interphase. However, the end products differ. Mitosis produces two genetically identical diploid somatic daughter cells. Meiosis produces four genetically unique haploid gametes. Student Misconceptions and Concerns • Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. Teaching Tips • How meiosis results in four haploid cells yet mitosis yields two diploid cells is often memorized but seldom understood. It can be explained like this. Consider a pair of chromosomes in a cell before any cell divisions. This pair of chromosomes duplicates such that two chromosomes become four (although each pair of sister chromatids are joined at their centromeres). Therefore, mitosis and meiosis each typically begin with four “chromosomes” after replication but before division. Mitosis divides once, producing two cells, each with two chromosomes. Meiosis divides twice, sorting the four chromosomes into four separate cells. • Consider emphasizing a crucial difference between the processes of mitosis and meiosis. In mitosis, sister chromatids separate at metaphase. In meiosis I metaphase, sister chromatids stay together, and homologous pairs of chromosomes separate. Consider sketching a comparison of the alignment of the chromosomes at mitosis metaphase and metaphase meiosis I. Module 8.14 helps to make this important distinction. You might create a test question in which you ask students to draw several pairs of homologous chromosomes lined up at metaphase in mitosis versus meiosis I. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Sister chromatids are separated
Figure MITOSIS MEIOSIS I Chromosomes are duplicated Chromosomes are duplicated Parent cell 2n = 4 Prophase Prophase I Homologous chromosomes pair up Homologous chromosomes remain separate Crossing over Metaphase Metaphase I Pairs of homologous chromosomes line up at the metaphase plate Chromosomes line up at the metaphase plate Anaphase Telophase Anaphase I Telophase I Homologous chromosomes are separated Figure Comparison of mitosis and meiosis (step 5) Sister chromatids are separated Sister chromatids remain attached 2n 2n n = 2 n = 2 MEIOSIS II Sister chromatids are separated n n n n

MITOSIS MEIOSIS I MEIOSIS II Figure 8.14-6
Figure Comparison of mitosis and meiosis (step 6) MEIOSIS II One division of the nucleus and cytoplasm Result: Two genetically identical diploid cells Used for: Growth, tissue repair, asexual reproduction Two divisions of the nucleus and cytoplasm Result: Four genetically unique haploid cells Used for: Sexual reproduction

8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Genetic variation in gametes results from independent orientation at metaphase I and random fertilization. Teaching Tips • The possible number of combinations produced by independent orientation of human chromosomes at meiosis metaphase I is 223, , or 8,388,608. This number squared is more than 70 trillion. The authors rounded down to 8 million for 223, and squared this, to estimate 64 trillion possible combinations. But more precisely, the number of possible zygotes produced by a single pair of reproducing humans, based solely on independent assortment and random fertilization, is over 70 trillion! • Another way to represent the various combinations produced by independent orientation of chromosomes at meiosis metaphase I is to continue the shoe analogy. Imagine that you have two pairs of shoes. One pair is black; the other is white. You want to make a new pair of shoes by drawing one shoe from each original pair. Four possible pairs can be made. You can have (1) the left black and left white, (2) the right black and right white, (3) the left black and right white, or (4) the right black and left white. Actually using two pairs of shoes from your students can inject humor and create a concrete example that reduces confusion. For an additional bit of humor, ask the class if 46 students want to contribute their shoes as you try to demonstrate all 8,388,608 combinations! Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Independent orientation at metaphase I Each pair of chromosomes independently aligns at the cell equator. There is an equal probability of the maternal or paternal chromosome facing a given pole. The number of combinations for chromosomes packaged into gametes is 2n, where n  haploid number of chromosomes. Teaching Tips • The possible number of combinations produced by independent orientation of human chromosomes at meiosis metaphase I is 223, , or 8,388,608. This number squared is more than 70 trillion. The authors rounded down to 8 million for 223, and squared this, to estimate 64 trillion possible combinations. But more precisely, the number of possible zygotes produced by a single pair of reproducing humans, based solely on independent assortment and random fertilization, is over 70 trillion! • Another way to represent the various combinations produced by independent orientation of chromosomes at meiosis metaphase I is to continue the shoe analogy. Imagine that you have two pairs of shoes. One pair is black; the other is white. You want to make a new pair of shoes by drawing one shoe from each original pair. Four possible pairs can be made. You can have (1) the left black and left white, (2) the right black and right white, (3) the left black and right white, or (4) the right black and left white. Actually using two pairs of shoes from your students can inject humor and create a concrete example that reduces confusion. For an additional bit of humor, ask the class if 46 students want to contribute their shoes as you try to demonstrate all 8,388,608 combinations! Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Random fertilization means that the combination of each unique sperm with each unique egg increases genetic variability. Teaching Tips • The possible number of combinations produced by independent orientation of human chromosomes at meiosis metaphase I is 223, , or 8,388,608. This number squared is more than 70 trillion. The authors rounded down to 8 million for 223, and squared this, to estimate 64 trillion possible combinations. But more precisely, the number of possible zygotes produced by a single pair of reproducing humans, based solely on independent assortment and random fertilization, is over 70 trillion! • Another way to represent the various combinations produced by independent orientation of chromosomes at meiosis metaphase I is to continue the shoe analogy. Imagine that you have two pairs of shoes. One pair is black; the other is white. You want to make a new pair of shoes by drawing one shoe from each original pair. Four possible pairs can be made. You can have (1) the left black and left white, (2) the right black and right white, (3) the left black and right white, or (4) the right black and left white. Actually using two pairs of shoes from your students can inject humor and create a concrete example that reduces confusion. For an additional bit of humor, ask the class if 46 students want to contribute their shoes as you try to demonstrate all 8,388,608 combinations! Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Two equally probable arrangements of chromosomes at
Figure Possibility A Possibility B Two equally probable arrangements of chromosomes at metaphase I Metaphase II Figure Results of the independent orientation of chromosomes at metaphase I (step 3) Gametes Combination 1 Combination 2 Combination 3 Combination 4

8.16 Homologous chromosomes may carry different versions of genes
Separation of homologous chromosomes during meiosis can lead to genetic differences between gametes. Homologous chromosomes may have different versions of a gene at the same locus. One version was inherited from the maternal parent and the other came from the paternal parent. Since homologous chromosomes move to opposite poles during anaphase I, gametes will receive either the maternal or paternal version of the gene. Teaching Tips • You might have some fun with the concept of different versions of genes. Playing with the pun “jeans,” ask students if all jeans are the same. (Some are stone washed, some have buttons instead of zippers, some have more pockets than others, etc.) These versions of clothing jeans are like different versions of genetic genes, representing options and sources of diversity. Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Tetrad in parent cell (homologous pair of duplicated chromosomes)
Figure Coat-color genes Eye-color genes C E Brown C Black E Brown coat (C); black eyes (E) C E Meiosis c e c e c e White Figure Differing genetic information (coat color and eye color) on homologous chromosomes Pink Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes White coat (c); pink eyes (e)

Tetrad in parent cell (homologous pair of duplicated chromosomes)
Figure Coat-color genes Eye-color genes C E Brown C Black E C E Meiosis c e c e c e White Pink Figure Differing genetic information (coat color and eye color) on homologous chromosomes (part 1) Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes

8.17 Crossing over further increases genetic variability
Genetic recombination is the production of new combinations of genes due to crossing over. Crossing over is an exchange of corresponding segments between nonsister chromatids of homologous chromosomes. Nonsister chromatids join at a chiasma (plural, chiasmata), the site of attachment and crossing over. Corresponding amounts of genetic material are exchanged between maternal and paternal (nonsister) chromatids. Teaching Tips • If you wish to continue the shoe analogy, crossing over is somewhat like exchanging the shoelaces in a pair of shoes (although this analogy is quite limited). A point to make is that the shoes (chromosomes) before crossing over are what you inherited either from the sperm or the egg; but, as a result of crossing over, you no longer pass along exactly what you inherited. Instead, you pass along a combination of homologous chromosomes (think of shoes with switched shoelaces). Critiquing this limited analogy may also help students to think through the process of crossing over. • In the shoe analogy, after exchanging shoelaces, we have “recombinant shoes”! • Challenge students to consider the number of unique humans that can be formed by the processes of the independent orientation of chromosomes, random fertilization, and crossing over. Without crossing over, we already calculated over 70 trillion possibilities. But as the text notes in Module 8.17, there are typically one to three crossover events for each human chromosome, and these can occur at many different places along the length of the chromosome. The potential number of combinations far exceeds any number that humans can comprehend, representing the truly unique nature of each human being (an important point that delights many students!). Active Lecture Tips • See the Activity Student Demonstration of Mitosis and Meiosis Using Chromosome Cut-Outs as Models on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Sister chromatids Chiasma Tetrad Figure 8.17a-0
Figure 8.17a-0 Chiasmata, the sites of crossing over Tetrad

Figure 8.17b-0 How crossing over leads to genetic recombination
Tetrad (pair of homologous chromosomes in synapsis) c e 1 Breakage of nonsister chromatids C E c e 2 Joining of nonsister chromatids C E Chiasma c e 3 Separation of homologous chromosomes at anaphase I C E C e c E c e Figure 8.17b-0 How crossing over leads to genetic recombination 4 Separation of chromatids at anaphase II and completion of meiosis C E Parental type of chromosome C e Recombinant chromosome c E Recombinant chromosome c e Parental type of chromosome Gametes of four genetic types

Figure 8.17b-1 C E Tetrad (pair of homologous chromosomes in synapsis) c e 1 Breakage of nonsister chromatids C E c e Figure 8.17b-1 How crossing over leads to genetic recombination (part 1) 2 Joining of nonsister chromatids C E Chiasma c e

Separation of homologous chromosomes at anaphase I
Figure 8.17b-2 C E Chiasma c e Separation of homologous chromosomes at anaphase I 3 C E C Figure 8.17b-2 How crossing over leads to genetic recombination (part 2) e c E c e

Separation of chromatids at anaphase II and completion of meiosis
Figure 8.17b-3 C E C e c E c e 4 Separation of chromatids at anaphase II and completion of meiosis C E Parental type of chromosome C e Recombinant chromosome Figure 8.17b-3 How crossing over leads to genetic recombination (part 3) c E Recombinant chromosome c e Parental type of chromosome Gametes of four genetic types

Alterations of Chromosome Number and Structure

8.18 Accidents during meiosis can alter chromosome number
Nondisjunction is the failure of chromosomes or chromatids to separate normally during meiosis. This can happen during meiosis I, if both members of a homologous pair go to one pole, or meiosis II, if both sister chromatids go to one pole. Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • Students might be confused by the term nondisjunction. But simply put, it is an error in the sorting of chromosomes during mitosis or meiosis. • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at © 2015 Pearson Education, Inc.

Meiosis I Nondisjunction Meiosis II Normal meiosis II Gametes
Figure Meiosis I Nondisjunction Meiosis II Normal meiosis II Figure Nondisjunction in meiosis I (part 1, step 3) Gametes Number of chromosomes n + 1 n + 1 n − 1 n − 1 Abnormal gametes

Meiosis I Normal meiosis I Meiosis II Nondisjunction n + 1 n − 1 n n
Figure Meiosis I Normal meiosis I Meiosis II Nondisjunction Figure Nondisjunction in meiosis II (part 2, step 3) n + 1 n − 1 n n Abnormal gametes Normal gametes

8.19 A karyotype is a photographic inventory of an individual’s chromosomes
A karyotype is an ordered display of magnified images of an individual’s chromosomes arranged in pairs. Karyotypes are often produced from dividing cells arrested at metaphase of mitosis and allow for the observation of homologous chromosome pairs, chromosome number, and chromosome structure. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at © 2015 Pearson Education, Inc.

Centromere Sister chromatids Pair of homologous chromosomes
Figure Centromere Sister chromatids Pair of homologous chromosomes Figure Preparation of a karyotype from a blood sample (part 3) Sex chromosomes

8.20 CONNECTION: An extra copy of chromosome 21 causes Down syndrome
Trisomy 21 involves the inheritance of three copies of chromosome 21 and is the most common human chromosome abnormality. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • If you have several hundred students or more in your class, it is likely that at least one of your students has a sibling with Down syndrome. The authors note that overall, about one in every 700 babies are born with Down syndrome. • The National Down Syndrome Society has a website at It is a wonderful resource. • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at Active Lecture Tips • See the Activity Applying the Concept of Non-Disjunction to Trisomy on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

8.20 CONNECTION: An extra copy of chromosome 21 causes Down syndrome
A person with trisomy 21 has a condition called Down syndrome, which produces a characteristic set of symptoms, including characteristic facial features, short stature, heart defects, susceptibility to respiratory infections, leukemia, and Alzheimer’s disease, and varying degrees of developmental disabilities. The incidence increases with the age of the mother. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • If you have several hundred students or more in your class, it is likely that at least one of your students has a sibling with Down syndrome. The authors note that overall, about one in every 700 babies are born with Down syndrome. • The National Down Syndrome Society has a website at It is a wonderful resource. • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at Active Lecture Tips • See the Activity Applying the Concept of Non-Disjunction to Trisomy on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

A person with Down syndrome
Figure 8.20a-0 Trisomy 21 Figure 8.20a-0 A karyotype showing trisomy 21 and an individual with Down syndrome A person with Down syndrome

Infants with Down syndrome (per 1,000 births)
Figure 8.20b 90 80 70 60 Infants with Down syndrome (per 1,000 births) 50 40 30 Figure 8.20b Maternal age and incidence of Down syndrome 20 10 20 25 30 35 40 45 Age of mother

8.21 CONNECTION: Abnormal numbers of sex chromosomes do not usually affect survival
Sex chromosome abnormalities seem to upset the genetic balance less than an unusual number of autosomes. This may be because of the small size of the Y chromosome or X chromosome inactivation. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • Some syndromes related to human sexuality are not the result of abnormalities in sex chromosome number. Androgen insensitivity syndrome produces sterile males who possess mostly female sex characteristics. People with this condition are genetically male but have bodies that fail to respond to male sex hormones. The National Institutes of Health website “Genetics Home Reference” can provide additional details about this and most genetic disorders at • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at © 2015 Pearson Education, Inc.

8.21 CONNECTION: Abnormal numbers of sex chromosomes do not usually affect survival
The following table lists the most common human sex chromosome abnormalities. In general, a single Y chromosome is enough to produce “maleness,” even in combination with several X chromosomes, and the absence of a Y chromosome yields “femaleness.” Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • Some syndromes related to human sexuality are not the result of abnormalities in sex chromosome number. Androgen insensitivity syndrome produces sterile males who possess mostly female sex characteristics. People with this condition are genetically male but have bodies that fail to respond to male sex hormones. The National Institutes of Health website “Genetics Home Reference” can provide additional details about this and most genetic disorders at • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at © 2015 Pearson Education, Inc.

Table 8.21 Table 8.21 Abnormalities of sex chromosome number in humans

8.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer
Chromosome breakage can lead to rearrangements that can produce genetic disorders or, if changes occur in somatic cells, cancer. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • Challenge students to create a simple sentence and then modify that sentence to represent (a) a deletion, (b) a duplication, and (c) an inversion as an analogy to these changes to a chromosome. • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at © 2015 Pearson Education, Inc.

These rearrangements can lead to four types of changes in chromosome structure. A deletion is the loss of a chromosome segment. A duplication is the repeat of a chromosome segment. An inversion is the reversal of a chromosome segment. A translocation is the attachment of a segment to a nonhomologous chromosome. A translocation may be reciprocal. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • Challenge students to create a simple sentence and then modify that sentence to represent (a) a deletion, (b) a duplication, and (c) an inversion as an analogy to these changes to a chromosome. • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at © 2015 Pearson Education, Inc.

Inversions are less likely than deletions or duplications to produce harmful effects, because in inversions all genes are still present in their normal number. Many deletions cause serious physical or mental problems. Translocations may or may not be harmful. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • Challenge students to create a simple sentence and then modify that sentence to represent (a) a deletion, (b) a duplication, and (c) an inversion as an analogy to these changes to a chromosome. • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at © 2015 Pearson Education, Inc.

Chronic myelogenous leukemia (CML) is one of the most common leukemias, affects cells that give rise to white blood cells (leukocytes), and results from a reciprocal translocation in which part of chromosome 22 switches places with a small fragment from a tip of chromosome 9. Such an exchange causes cancer by activating a gene that leads to uncontrolled cell cycle progression. Because the chromosomal changes in cancer are usually confined to somatic cells, cancer is not usually inherited. Student Misconceptions and Concerns • Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23. Teaching Tips • Challenge students to create a simple sentence and then modify that sentence to represent (a) a deletion, (b) a duplication, and (c) an inversion as an analogy to these changes to a chromosome. • The Human Genome website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at © 2015 Pearson Education, Inc.

Reciprocal translocation
Figure 8.23a-0 Deletion Inversion Duplication Reciprocal translocation Homologous chromosomes Figure 8.23a-0 Alterations of chromosome structure Nonhomologous chromosomes

Reciprocal translocation Chromosome 22
Figure 8.23b Chromosome 9 Reciprocal translocation Chromosome 22 Figure 8.23b The translocation associated with chronic myelogenous leukemia Activated cancer-causing gene

Genetically identical daughter cells M Cytokinesis G2 Mitosis
Figure 8.UN01 S G1 (DNA synthesis) Genetically identical daughter cells M Cytokinesis G2 Mitosis Figure 8.UN01 Reviewing the concepts, 8.4 Cytokinesis (division of the cytoplasm) Mitosis (division of the nucleus)

n n 2n Haploid gametes (n = 23) Egg cell n n Sperm cell Meiosis
Figure 8.UN02 Haploid gametes (n = 23) Egg cell n n n n Sperm cell Meiosis Fertilization Human life cycle Figure 8.UN02 Reviewing the concepts, 8.12 2n 2n Multicellular diploid adults (2n = 46) Diploid zygote (2n = 46) Mitosis

Figure 8.UN03 Figure 8.UN03 Connecting the concepts, question 1

Figure 8.UN04 Figure 8.UN04 Testing your knowledge, question 12

© 2015 Pearson Education, Inc.

Similar presentations

Presentation on theme: "© 2015 Pearson Education, Inc."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

© 2015 Pearson Education, Inc.

Similar presentations

Presentation on theme: "© 2015 Pearson Education, Inc."— Presentation transcript:

Similar presentations

About project

Feedback