Making More By Yourself: Mitosis CHAPTER 8 The Need for Cell Reproduction The Nature of Chromosomes The Cell Cycle Mitosis and Cytokinesis Prophase Metaphase Anaphase Telophase Cytokinesis Cancer Cells: Abnormal Cell Cycle

What Cell Reproduction Accomplishes Reproduction –The birth of new organisms. –Occurs much more often at the cellular level Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings Cell division plays a role in –The replacement of lost or damaged cells. –Cell reproduction and growth.

Passing On Genes from Cell to Cell Before a parent cell divides, it duplicates its chromosomes. The two resulting “daughter” cells are genetically identical, each getting a duplicate set of chromosomes

Types of Reproduction Asexual reproduction –Single cells reproduce by mitosis –Two daughter cells produced from one parent cell Daughter cells are genetically identical to each other Daughter cells are genetically identical to the parent cell Sexual reproduction –Single or multi-celled organisms reproduce by meiosis –Four daughter cells called gametes (eggs and sperm) produced from one parent cell Gametes are genetically different from each other and parent cell Gametes must unite with other gametes of opposite type to produce viable organism –Use for growth and repair as well as producing new individuals –Finding a mate is unnecessary –Relatively “cheap” energetically –Used solely for making more individual single or multicellular organisms –A mate or a second organ for producing other gametes is required –Relatively “expensive” energetically; lower efficiency in producing offspring

Type of Asexual Reproduction Budding (as in Hydra)Hydra Sprouting Regeneration Binary fission

Both Daughter Cells in Mitosis Must Get Chromosomes 12 chromosomes 12 chromosomes 12 chromosomes ? chromosomes Duplication (Replication)

Replication (Duplication) Occurs in S Phase of the Cell Cycle

Figure 8.7 The Cell Cycle G1G1 G2G2 S M

Chromosomes Must Be Condensed or Packaged Before Cell Division DNA Packing

Figure 8.4 DNA loosely wound in nucleus DNA beginning to wind up (condense) in nucleus

Mitosis Overview Prophase Metaphase Anaphase Telophase/ Cytokinesis Mitosis (All Phases) Animal Mitosis Sea Urchin (time lapse)

Figure G 2 of Interphase: Chromosomes indistinct Centrosomes replicate Mitosis Overview To M Phase: 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase and Cytokinesis Late Interphase

Figure Chromosomes condense, become visible 2. Nuclear membrane dissolves 3. Centrioles move to opposite poles, grow fibers 1. Chromosomes line up in a column 90 o to spindle Prophase Prometaphase Metaphase

1. Sister chromatids separate and move towards opposite poles 2. Two nuclear membranes reform 3. Cell divides in half (cytokinesis) 1. Chromosomes unwind (decondense) AnaphaseTelophase

Cytokinesis –Typically occurs during telophase. –Is the division of the cytoplasm. –Is different in plant and animal cells. Cytokinesis Cell Splitting in Telophase: Cytokinesis

Mitosis Overview Prophase Metaphase Anaphase Telophase/ Cytokinesis Mitosis (All Phases) Animal Mitosis Sea Urchin (time lapse)

Cancer Cells: Growing Out of Control Normal plant and animal cells have a cell cycle control system. Cancer is a disease of the cell cycle. Cancer cells do not respond normally to the cell cycle control system. Cancer cells can form tumors, –Abnormally growing masses of body cells. If a tumor is malignant and metastasizes it can spread to other parts of the body.

Figure 8.10 Breast Cancer

Cancer Prevention and Survival Cancer prevention includes changes in lifestyle: –Not smoking –Exercising adequately –Avoiding exposure to the sun –Eating a high-fiber, low-fat diet –Visiting the doctor regularly –Performing regular self-examinations

Making More With a Partner: Meiosis CHAPTER 8 Overview of Sexual Reproduction Homologous Chromosomes Gametes and Sexual Life Cycle Steps of Meiosis – Meiosis I Synapsis and crossing over – Meiosis II Comparing Mitosis and Meiosis How Genetic Variation Arises Faulty Meiosis/Chromosome Abnormalities

Types of Reproduction Asexual reproduction –Single cells reproduce by mitosis –Two daughter cells produced from one parent cell –Daughter cells identical (clones) and just like the parent cell –Use for growth and repair as well as producing new individuals –Relatively cheap energetically, no mate necessary –Great for producing large numbers of offspring equally adapted to environment as parent Sexual reproduction –Single or multi-celled organisms reproduce by meiosis –Four daughter cells called gametes (eggs and sperm) produced from one parent cell Gametes are genetically different from each other and parent cell Gametes must unite with other gametes of opposite type to produce viable organism –Used solely for making more individual single or multicellular organisms –A mate or a second organ for producing other gametes is required –Relatively “expensive” energetically; lower efficiency in producing offspring –Essential for producing offspring with a large range of variation; impt. for species survival

Figure 8.12 Sexually Reproducing Species Exhibit Substantial Individual Variation

Making More With a Partner: Meiosis CHAPTER 8 Overview of Sexual Reproduction Homologous Chromosomes Gametes and Sexual Life Cycle Steps of Meiosis – Meiosis I Synapsis and crossing over – Meiosis II Comparing Mitosis and Meiosis How Genetic Variation Arises Faulty Meiosis/Chromosome Abnormalities

Homologous Chromosomes (Pairs) Sexually reproducing organisms have chromosomes that can be organized into pairs Each pair member is called a homologous chromosome to the other Homologous chromosomes are the same length, have the same banding pattern, have centromeres located in the same places, and carry similar genes for the same traits. One of every homologous pair comes from your father, the other comes from your mother Paternal Maternal chromosome chromosome

Meiosis: One of every homologous pair is removed Chromosome number needs to be cut in half first before fertilization Making Sex Cells Must Involve Chromosome Reduction Diploid state (2n ) Haploid state (1n ) Half set of chromosomes present; only one of each homologous pair Full set of chromosomes present; both chromosomes of each pair in cell First generationSecond generationThird generation

Making More With a Partner: Meiosis CHAPTER 8 Overview of Sexual Reproduction Homologous Chromosomes Gametes and Sexual Life Cycle Steps of Meiosis – Meiosis I Synapsis and crossing over – Meiosis II Comparing Mitosis and Meiosis How Genetic Variation Arises Faulty Meiosis/Chromosome Abnormalities

Figure 8.15 Meiosis Consists of Two Phases, Meiosis I and Meiosis II

The Process of Meiosis Meiosis I –Chromosomes exchange segments (crossing over) to produce new and unique combinations of genes –Homologous (replicated) chromosome pairs separate and move to 2 different cells Meiosis Overview Meiosis II –Chromatids of each replicated chromosome separate and move into two different cells –Two cells from Meiosis I become four cells at the end of Meiosis II

Figure Interphase: Chromosomes replicate Centrioles duplicate

Figure Prophase I Metaphase IAnaphase I Telophase I & Cytokinesis 1.Chromosomes condense 2.Centrioles move to opposite poles 3.Nuclear membrane dissolves 4.Homologous chromosomes synapse and exchange genetic material (crossing over) Replicated homologous chromosomes line up as pairs down the middle of the cell Replicated homologous chromosomes separate from each other and move to opposite poles (chromatids do not separate) 1.Cytokinesis occurs, forming two cells 2.Nuclear membrane may briefly reform 3.Chromosomes usually stay condensed 4.Centrioles replicate in each cell Cells are now haploid (2n) Crossing Over

Telophase II & Cytokinesis Prophase IIMetaphase IIAnaphase II 1.Chromosomes condense if they unwound at all 2.Centrioles move to opposite poles 3.Nuclear membrane dissolves Replicated chromosomes line up singly perpendicular to the spindle Chromatids (no longer identical) separate and move to opposite poles 1.Cytokinesis occurs in each cell forming four gametes 2.Nuclear membranes reform 3.Chromosomes unwind (decondense) None of these cells is genetically identical to the others

Making More With a Partner: Meiosis CHAPTER 8 Overview of Sexual Reproduction Homologous Chromosomes Gametes and Sexual Life Cycle Steps of Meiosis – Meiosis I Synapsis and crossing over – Meiosis II Comparing Mitosis and Meiosis How Genetic Variation Arises Faulty Meiosis/Chromosome Abnormalities

Figure 8.17 Comparing Mitosis to Meiosis -Parent cell divides to produce genetically identical daughter cells -The number of chromosomes stays the same -Only one division -Parent cell divides to produce genetically different cells (variation introduced) -The number of chromosomes is cut in half during the process -Two divisions occur

The Three Ways Genetic Variation is Introduced Offspring of sexual reproduction are genetically different from their parents and from one another. 2. Variation is also introduced through the different ways in which homologous chromosomes can separate in Anaphase I (called independent assortment) Genetic Variation 1. Some of the variation introduced in meiosis occurs during the recombination of genes in Prophase I (crossing over) 3. The human egg cell is then fertilized randomly by one sperm, leading to genetic variety in the zygote.

Figure 8.19 Crossing Over Crossing Over Produces New Gene Combinations

Figure 8.18 Independent Assortment in Metaphase/Anaphase I Yields Different Combinations

Making More With a Partner: Meiosis CHAPTER 8 Overview of Sexual Reproduction Homologous Chromosomes Gametes and Sexual Life Cycle Steps of Meiosis – Meiosis I Synapsis and crossing over – Meiosis II Comparing Mitosis and Meiosis How Genetic Variation Arises Faulty Meiosis/Chromosome Abnormalities

When Meiosis Goes Awry Nondisjunction –Members of a chromosome pair fail to separate during anaphase. –Gametes with an incorrect number of chromosomes are produced. –Nondisjunction can occur in Meiosis I or II

Figure 8.20 Examples and Results of Nondisjunction

Figure 8.21 Fertilization of Abnormal Egg with Normal Sperm Trisomy (3 copies) of long chromosome

Figure 8.22 Down Syndrome: An Extra Chromosome 21 Results from nondisjunction of egg or sperm, incidence rises if mother is over 35

Figure 8.23 Incidence of Nondisjunction Rises When Eggs Sit Suspended in Prophase I Too Long

Table 8.1 Nondisjunction and Abnormalities in Sex Chromosome Number

Evolution Connection: New Species from Errors in Cell Division Errors in meiosis may have been instrumental in the evolution of many species. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings Polyploidy –Cells have two or more sets of homologous chromosomes in each somatic cell –Most common in plants, usually fatal in animals –Polyploids are different species compared to their diploid ancestors

Making More With a Partner: Meiosis CHAPTER 8 Overview of Sexual Reproduction Homologous Chromosomes Gametes and Sexual Life Cycle Steps of Meiosis – Meiosis I Synapsis and crossing over – Meiosis II Comparing Mitosis and Meiosis How Genetic Variation Arises Faulty Meiosis/Chromosome Abnormalities