Chapter 8 The Cellular Basis of Reproduction and Inheritance Cancer cells start out as normal body cells, undergo genetic mutations, lose the ability to control the tempo of their own division, and run amok, causing disease. © 2012 Pearson Education, Inc. 1

Introduction In a healthy body, cell division allows for In a healthy body, cell division allows for growth, the replacement of damaged cells, and development from an embryo into an adult. In sexually reproducing organisms, eggs and sperm result from mitosis and meiosis. © 2012 Pearson Education, Inc. 2

CELL DIVISION AND REPRODUCTION © 2012 Pearson Education, Inc. 3

8.1 Cell division plays many important roles in the lives of organisms Organisms reproduce their own kind, a key characteristic of life. Cell division is reproduction at the cellular level, requires the duplication of chromosomes, and sorts new sets of chromosomes into the resulting pair of daughter cells. © 2012 Pearson Education, Inc. 4

8.1 Cell division plays many important roles in the lives of organisms 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 sperm and egg production. © 2012 Pearson Education, Inc. 5

8.1 Cell division plays many important roles in the lives of organisms 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. © 2012 Pearson Education, Inc. 6

Figure 8.1A Yeast cell asexually reproducing Figure 8.1A A yeast cell producing a genetically identical daughter cell by asexual reproduction 7

Figure 8.1B Sea star reproducing asexually Figure 8.1B A sea star reproducing asexually 8

Figure 8.1C African violet leaf cutting reproducing asexually Figure 8.1C An African violet reproducing asexually from a cutting (the large leaf on the left) 9

Figure 8.1D Sexual reproduction produces offspring that are similar to the parents, but show variations in traits Figure 8.1D Sexual reproduction produces offspring with unique combinations of genes. 10

8.2 Prokaryotes reproduce by binary fission Prokaryotes (bacteria and archaea) reproduce by binary fission (“dividing in half”). The chromosome of a prokaryote is a singular circular DNA molecule associated with proteins and much smaller than those of eukaryotes. © 2012 Pearson Education, Inc. 11

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. © 2012 Pearson Education, Inc. 12

Duplication of the chromosome and separation of the copies Figure 8.2A_s1 Plasma membrane Prokaryotic chromosome Cell wall Duplication of the chromosome and separation of the copies 1 Figure 8.2A_s1 Binary fission of a prokaryotic cell (step 1) 13

Duplication of the chromosome and separation of the copies Figure 8.2A_s2 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_s2 Binary fission of a prokaryotic cell (step 2) 14

Division into two daughter cells Figure 8.2A 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_s3 Binary fission of a prokaryotic cell (step 3) Division into two daughter cells 3 15

THE EUKARYOTIC CELL CYCLE AND MITOSIS © 2012 Pearson Education, Inc. 16

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. © 2012 Pearson Education, Inc. 17

8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division 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. © 2012 Pearson Education, Inc. 18

Figure 8.3A A plant cell (from an African blood lily) just before cell division 19

Chromosomes DNA molecules Sister chromatids Chromosome duplication Figure 8.3B Chromosomes DNA molecules Sister chromatids Chromosome duplication Sister chromatids Centromere Figure 8.3B Chromosome duplication and distribution Chromosome distribution to the daughter cells 20

8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division Before a eukaryotic cell begins to divide, it duplicates all of its chromosomes, resulting in two copies called sister chromatids joined together by a narrowed “waist” called the centromere. When a cell divides, the sister chromatids separate from each other, now called chromosomes, and sort into separate daughter cells. © 2012 Pearson Education, Inc. 21

8.4 The cell cycle multiplies cells 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. © 2012 Pearson Education, Inc. 22

8.4 The cell cycle multiplies cells 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 © 2012 Pearson Education, Inc. 23

I N T E R P H A S G1 (first gap) S (DNA synthesis) M G2 (second gap) Figure 8.4 I N T E R P H A S G1 (first gap) S (DNA synthesis) M Cytokinesis G2 (second gap) Mitosis Figure 8.4 The eukaryotic cell cycle T MI O IC PH A SE 24

8.5 Cell division is a continuum of dynamic changes Mitosis progresses through a series of stages: prophase, metaphase, anaphase, and telophase. Cytokinesis occurs at end of telophase. © 2012 Pearson Education, Inc. 25

8.5 Cell division is a continuum of dynamic changes A mitotic spindle is required to divide the chromosomes, composed of microtubules, and produced by centrosomes, structures in the cytoplasm that organize microtubule arrangement and contain a pair of centrioles in animal cells. © 2012 Pearson Education, Inc. 26

(with centriole pairs) Fragments of the nuclear envelope Early mitotic Figure 8.5 MITOSIS INTERPHASE Prophase Prometaphase Centrosomes (with centriole pairs) Fragments of the nuclear envelope Early mitotic spindle Centrosome Kinetochore Centrioles Chromatin Figure 8.5_1 The stages of cell division by mitosis: Interphase through Prometaphase Centromere Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Spindle microtubules 27

8.5 Cell division is a continuum of dynamic changes Interphase The cytoplasmic contents double in G phases, two centrosomes containing ____ form, chromatin duplicates in the nucleus during the S phase © 2012 Pearson Education, Inc. 28

8.5 Cell division is a continuum of dynamic changes Prophase In the cytoplasm microtubules begin to emerge from centrosomes, forming the ____. In the nucleus chromatin coils and becomes compact to form ____. © 2012 Pearson Education, Inc. 29

8.5 Cell division is a continuum of dynamic changes Metaphase Spindle microtubules reach chromosomes, where they attach on the centromeres and move ____ to the center of the cell The nuclear envelope disappears. ____ align at the cell equator. © 2012 Pearson Education, Inc. 30

(with centriole pairs) Early mitotic spindle Fragments of Figure 8.5 MITOSIS INTERPHASE Prophase Prometaphase Centrosomes (with centriole pairs) Early mitotic spindle Fragments of the nuclear envelope Centrosome Chromatin Centrioles Kinetochore Figure 8.5_left The stages of cell division by mitosis: Interphase through Prometaphase Nuclear envelope Plasma membrane Centromere Chromosome, consisting of two sister chromatids Spindle microtubules 31

Telophase and Cytokinesis Figure 8.5 MITOSIS Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Figure 8.5_right The stages of cell division by mitosis: Metaphase through Cytokenesis Mitotic spindle Nuclear envelope forming Daughter chromosomes 32

8.5 Cell division is a continuum of dynamic changes Anaphase Sister chromatids separate at the centromeres. Daughter chromosomes are moved to opposite poles of the cell as ____ shortens. © 2012 Pearson Education, Inc. 33

Figure 8.5 Figure 8.5_7 The stages of cell division by mitosis: Anaphase Anaphase 34

8.5 Cell division is a continuum of dynamic changes Telophase The cell continues to elongate. The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei. Chromosomes uncoil to form ____. The spindle breaks down. © 2012 Pearson Education, Inc. 35

Telophase and Cytokinesis Figure 8.5 Figure 8.5_8 The stages of cell division by mitosis: Telophase and Cytokenesis Telophase and Cytokinesis 36

8.5 Cell division is a continuum of dynamic changes During cytokinesis, the cytoplasm is divided into separate cells. The process of cytokinesis differs in animal and plant cells. Teaching Tips Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. © 2012 Pearson Education, Inc. 37

8.6 Cytokinesis differs for plant and animal cells In animal cells, cytokinesis occurs as a cleavage ____ forms and deepens to separate the contents into two cells. © 2012 Pearson Education, Inc. 38

Cleavage furrow Daughter cells Figure 8.6A Cytokinesis Cleavage furrow Daughter cells Figure 8.6A Cleavage of an animal cell Cleavage furrow 39

8.6 Cytokinesis differs for plant and animal cells In plant cells, cytokinesis occurs as a cell plate forms in the middle the cell plate grows outward to reach the edges, dividing the contents into two cells, each cell now possesses a plasma membrane and cell ____. © 2012 Pearson Education, Inc. 40

Cytokinesis New cell wall Cell wall of the parent cell Cell wall Figure 8.6B Cytokinesis New cell wall Cell wall of the parent cell Cell wall Plasma membrane Daughter nucleus Vesicles containing cell wall material Cell plate Daughter cells Figure 8.6B Cell plate formation in a plant cell Cell plate forming 41

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 and other industrialized nations. Cancer cells escape controls on the cell cycle. Cancer cells Undergo mitosis rapidly spread to other tissues through the circulatory system, and grow without being inhibited by other cells. © 2012 Pearson Education, Inc. 42

8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors A tumor is an abnormally growing mass of body cells. Benign tumors remain at the original site. Malignant tumors spread to other locations, called metastasis. © 2012 Pearson Education, Inc. 43

Lymph vessels Blood vessel Tumor Tumor in 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 Growth Invasion Metastasis 44

8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors Cancer treatments Localized tumors can be removed surgically and/or treated with concentrated beams of high-energy radiation. Chemotherapy is used for metastatic tumors. © 2012 Pearson Education, Inc. 45

8.10 Review: Mitosis provides for growth, cell replacement, and asexual reproduction When the cell cycle operates normally, mitosis produces genetically identical cells for growth, replacement of damaged and lost cells, and asexual reproduction. © 2012 Pearson Education, Inc. 46

Laboratory--Onion growing by mitosis Figure 8.10A Growth (in an onion root) 47

MEIOSIS AND CROSSING OVER © 2012 Pearson Education, Inc. 48

8.11 Chromosomes are matched in homologous pairs In humans, somatic cells have 23 pairs of homologous chromosomes and one member of each pair from each parent. 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. © 2012 Pearson Education, Inc. 49

8.11 Chromosomes are matched in homologous pairs Homologous chromosomes are matched in length, centromere position, and gene locations. A locus (plural, loci) is the position of a gene. Different versions of a gene may be found at the same locus on maternal and paternal chromosomes. © 2012 Pearson Education, Inc. 50

Pair of homologous chromosomes One duplicated chromosome Figure 8.11 Pair of homologous chromosomes Locus Centromere Sister chromatids Figure 8.11 A pair of homologous chromosomes One duplicated chromosome 51

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, with body cells that have two sets of chromosomes, one from each parent. © 2012 Pearson Education, Inc. 52

8.12 Gametes have a single set of chromosomes Meiosis is a process that converts diploid nuclei to haploid nuclei. Diploid cells have two homologous sets of chromosomes. Haploid cells have one set of chromosomes. Meiosis occurs in the sex organs, producing gametes—sperm and eggs. Fertilization is the union of sperm and egg. The zygote has a diploid chromosome number, one set from each parent. © 2012 Pearson Education, Inc. 53

Multicellular diploid adults (2n  46) Diploid stage (2n) Figure 8.12A Haploid gametes (n  23) n Egg cell n Sperm cell Meiosis Fertilization Ovary Testis Figure 8.12A The human life cycle Diploid zygote (2n  46) 2n Key Mitosis Haploid stage (n) Multicellular diploid adults (2n  46) Diploid stage (2n) 54

8.12 Gametes have a single set of chromosomes All sexual life cycles include an alternation between a diploid stage and a haploid stage. Producing haploid gametes prevents the chromosome number from doubling in every generation. © 2012 Pearson Education, Inc. 55

Sister chromatids A pair of homologous chromosomes in a diploid Figure 8.12B INTERPHASE MEIOSIS I MEIOSIS II Sister chromatids 1 2 3 A pair of homologous chromosomes in a diploid parent cell A pair of duplicated homologous chromosomes Figure 8.12B How meiosis halves chromosome number 56

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 combine in fertilization to restore the diploid state in the zygote. © 2012 Pearson Education, Inc. 57

8.13 Meiosis reduces the chromosome number from diploid to haploid 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. © 2012 Pearson Education, Inc. 58

8.13 Meiosis reduces the chromosome number from diploid to haploid Meiosis I – Prophase I – events occurring in the nucleus. Chromosomes coil and become compact. Homologous chromosomes come together as pairs Each pair, with four chromatids, is called a tetrad. Tetrads exchange genetic material by crossing over. © 2012 Pearson Education, Inc. 59

MEIOSIS I: Homologous chromosomes separate Figure 8.13 MEIOSIS I: Homologous chromosomes separate INTERPHASE: Chromosomes duplicate Prophase I Metaphase I Anaphase I Centrosomes (with centriole pairs) Spindle microtubules attached to a kinetochore Sister chromatids remain attached Sites of crossing over Centrioles Spindle Tetrad Figure 8.13_left The stages of meiosis: Interphase and Meiosis I Nuclear envelope Chromatin Sister chromatids Centromere (with a kinetochore) Metaphase plate Fragments of the nuclear envelope Homologous chromosomes separate 60

8.13 Meiosis reduces the chromosome number from diploid to haploid 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. © 2012 Pearson Education, Inc. 61

8.13 Meiosis reduces the chromosome number from diploid to haploid Meiosis I – Telophase I Duplicated chromosomes have reached the poles. A nuclear envelope re-forms around chromosomes in some species. Each nucleus has the haploid number of chromosomes. © 2012 Pearson Education, Inc. 62

8.13 Meiosis reduces the chromosome number from diploid to haploid Meiosis II follows meiosis I without chromosome duplication. Each of the two haploid products enters meiosis II. Meiosis II – Prophase II Chromosomes coil and become compact (if uncoiled after telophase I). Nuclear envelope, if re-formed, breaks up again. © 2012 Pearson Education, Inc. 63

Figure 8.13 MEIOSIS II: Sister chromatids separate Telophase II and Cytokinesis Telophase I and Cytokinesis Prophase II Metaphase II Anaphase II Cleavage furrow Sister chromatids separate Haploid daughter cells forming Figure 8.13_right The stages of meiosis: Telophase I and Meiosis II 64

8.13 Meiosis reduces the chromosome number from diploid to haploid Meiosis II – Metaphase II – Duplicated chromosomes align at the cell equator. Meiosis II – Anaphase II Sister chromatids separate and chromosomes move toward opposite poles. © 2012 Pearson Education, Inc. 65

8.13 Meiosis reduces the chromosome number from diploid to haploid 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. © 2012 Pearson Education, Inc. 66

8.14 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. © 2012 Pearson Education, Inc. 67

Sister chromatids are separated Figure 8.14 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 8.14 Comparison of mitosis and meiosis Sister chromatids are separated Sister chromatids remain attached 2n 2n n = 2 n = 2 MEIOSIS II Sister chromatids are separated n n n n 68

MITOSIS MEIOSIS I MEIOSIS II Figure 8.14 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. © 2012 Pearson Education, Inc. 70

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. © 2012 Pearson Education, Inc. 71

8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Random fertilization – The combination of each unique sperm with each unique egg increases genetic variability. © 2012 Pearson Education, Inc. 72

Two equally probable arrangements of chromosomes at metaphase I Figure 8.15 Possibility A Possibility B Two equally probable arrangements of chromosomes at metaphase I Figure 8.15_s1 Results of the independent orientation of chromosomes at metaphase I (step 1) 73

Two equally probable arrangements of chromosomes at metaphase I Figure 8.15 Possibility A Possibility B Two equally probable arrangements of chromosomes at metaphase I Metaphase II Figure 8.15_s2 Results of the independent orientation of chromosomes at metaphase I (step 2) 74

Two equally probable arrangements of chromosomes at metaphase I Figure 8.15 Possibility A Possibility B Two equally probable arrangements of chromosomes at metaphase I Metaphase II Figure 8.15_s3 Results of the independent orientation of chromosomes at metaphase I (step 3) Gametes Combination 1 Combination 2 Combination 3 Combination 4 75

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 homologues move to opposite poles during ____ I, gametes will receive either the maternal or paternal version of the gene. © 2012 Pearson Education, Inc. 76

duplicated chromosomes) Figure 8.16 Coat-color genes Eye-color genes C E Brown Black Brown coat (C); black eyes (E) C E C E Meiosis c e c Figure 8.16 Differing genetic information (coat color and eye color) on homologous chromosomes e c e White Pink Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes White coat (c); pink eyes (e) 77

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 chromatids on homologous chromosomes. Corresponding amounts of genetic material are exchanged between maternal and paternal chromatids. © 2012 Pearson Education, Inc. 78

Chiasma Sister chromatids Figure 8.17a-0 Figure 8.17A-B Tetrad (pair of homologous chromosomes in synapsis) c e 1 Breakage of homologous chromatids Chiasma C E c e 2 Joining of homologous chromatids C E Sister chromatids c e 3 Separation of homologous chromosomes at anaphase I C E C e c E Figure 8.17B How crossing over leads to genetic recombination c e Separation of chromatids at anaphase II and completion of meiosis 4 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 79

ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE © 2012 Pearson Education, Inc. 80

8.18 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. © 2012 Pearson Education, Inc. 81

Figure 8.19 Figure 8.18_s4 Preparation of a karyotype from a blood sample (step 4) 4 82

Centromere Sister chromatids Pair of homologous chromosomes Figure 8.19 Centromere Sister chromatids Pair of homologous chromosomes Figure 8.18_s5 Preparation of a karyotype from a blood sample (step 5) 5 Sex chromosomes 83

8.19 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. © 2012 Pearson Education, Inc. 84

8.19 CONNECTION: An extra copy of chromosome 21 causes Down syndrome Trisomy 21, called Down syndrome, produces a characteristic set of symptoms, which include: mental retardation, characteristic facial features, short stature, heart defects, susceptibility to respiratory infections, leukemia, and Alzheimer’s disease, and shortened life span. The incidence increases with the age of the mother. © 2012 Pearson Education, Inc. 85

A person with Down syndrome Figure 8.20A Trisomy 21 Figure 8.19A A karyotype showing trisomy 21, and an individual with Down syndrome A person with Down syndrome 86

Infants with Down syndrome Figure 8.20B 90 80 70 60 50 Infants with Down syndrome (per 1,000 births) 40 30 Figure 8.19B Maternal age and incidence of Down syndrome 20 10 20 25 30 35 40 45 50 Age of mother 87

Figure from Laboratory Figure 8.UN04 Testing Your Knowledge, question 12 88