Chapter 4 Mitosis & Meiosis OM.ppt PDF

PowerPoint to accompany Genetics: From Genes to Genomes Fourth Edition Leland H. Hartwell, Leroy Hood, Michael L. Goldberg, Ann E. Reynolds, and Lee M. Silver Prepared by Mary A. Bedell University of Georgia Copyright © The McGraw-Hill Companies, Inc....

PowerPoint to accompany Genetics: From Genes to Genomes Fourth Edition Leland H. Hartwell, Leroy Hood, Michael L. Goldberg, Ann E. Reynolds, and Lee M. Silver Prepared by Mary A. Bedell University of Georgia Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 1 PART I Basic Principles: How Traits Are Transmitted CHAPTER CHAPTER CHAPTER CHAPTER The Chromosome Theory of Inheritance CHAPTER OUTLINE  4.1 Chromosomes: The Carriers of Genes  4.2 Mitosis: Cell Division That Preserves Chromosome Number  4.3 Meiosis: Cell Divisions That Halve Chromosome Number  4.4 Gametogenesis  4.5 Validation of the Chromosome Theory Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 2 4th ed., Chapter 4  Chromosomes are cellular structures that transmit genetic information  Breeding experiments and microscopy provided evidence for the chromosome theory of inheritance  Proper development relies on accurately passing ono genes and accurate maintenance of chromosome number  The abstract idea of a gene was changed to a physical reality by the chromosome theory Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 3 4th ed., Chapter 4  Evidence that genes reside in chromosomes  Mitosis – process that generates 2 daughter cells containing the same number and type of chromosomes/genes as parent cell. In other words, the 2 daughter cells are identical to each other to the parent cell. Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4 4th ed., Chapter 4  Evidence that genes reside in chromosomes  Mitosis – process that generates 2 daughter cells containing the same number and type of chromosomes/genes as parent cell. In other words, the 2 daughter cells are identical to each other to the parent cell.  Meiosis – process that generates gametes (= egg and sperm cell) that have 1/2 the number of chromosomes compared to the parent cell. For instance, in humans: 46 chromosomes 23 chromosomes (parent cell) (gamete: sperm or egg cell) Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 5 4th ed., Chapter 4  Diploid versus haploid: 2n versus n  Most body cells are diploid (chromosomes are in pairs: one copy from mother and one copy from father)  Meiosis: diploid (2n)  haploid (n) gametes (= egg and sperm cells) In humans , 2n = 46 and n = 23, In Drosophila, 2n = 8, n = 4 Diploid = double set of chromosomes Haploid = 1 set of chromosomes Fig. 4.2 6 Fertilization is the union of haploid gametes to produce diploid zygotes 7 Metaphase chromosomes can be classified by centromere position Fig. 4.3 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4th ed., Chapter 4 8 Human Karyotype 9  Homologous chromosomes are matched in size, shape , and banding patterns  Homologs (= homologous pairs of chromosomes) contain the same set of genes, but can have different alleles for some genes  Non-homologs carry completely unrelated sets of genes  Karyotype – micrograph (photo) of stained chromosomes arranged in homologous pairs (see Fig 4.4) Sex chromosomes – unpaired X and Y chromosome Autosomes – all chromosomes except X and Y  Cells of each species have a characteristic diploid number of chromosomes  e.g. D. melanogaster, 2n = 8; D. obscura, 2n = 10; D. virilis, 2n = 12; sweet peas, 2n = 14; goldfish, 2n = 94; dogs, 2n = 78 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 10 4th ed., Chapter 4  Karyotype of a human male  The chromosomes visible only at the metaphase stage of mitosis (more condensed).  22 homologous pairs of autosomes and two sex chromosomes.  Each chromosome has a characteristic size and shape in the “normal” cell Photos of metaphase human chromosomes (2n = 46, n = 23) Fig. 4.4 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 11 4th ed., Chapter 4  The X and Y chromosomes determine sex in humans Children receive an X chromosome from their mother, but either an X or Y chromosome from their father Results in 1:1 ratio of females-to-males Fig. 4.6 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 12 4th ed., Chapter 4 Mechanisms of sex determination differ between species Homogametic vs heterogametic Table 4.2 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 13 4th ed., Chapter 4 California Sheepshead Photo: Male Sheephead Monterey Bay Aquarium, Oliver Manlik 14  Mitosis has five stages that have distinct cytological characteristics Interphase: DNA replication (and transcription) The five stages of mitosis and their major events: Prophase – chromatin condenses to form chromosomes Prometaphase – spindle forms and sister chromatids attach to microtubules from opposite centrosomes Metaphase – chromosome line up at the metaphase plate Anaphase – sister chromatids separate and move to opposite poles Telophase – chromosomes decondense (form chromatin) and nuclei form again Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 15 4th ed., Chapter 4  Stages of mitosis: Prophase  Chromosomes form (condense) and become visible  Centrosomes (pairs of centrioles) start to move toward opposite poles  Nucleolus comes apart Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 16 4th ed., Chapter 4  Stages of Mitosis: Prometaphase  Nuclear envelope breaks down, nucleus comes apart  Mitotic spindle starts to forms: Spindle fibers (microtubules) extend from centrosomes and connect to kinetochores at centromere region of each chromatid. Centrosomes are at or near opposite poles Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 17 4th ed., Chapter 4  Stages of mitosis: metaphase  Chromosomes line up one by one at the metaphase plate with sister chromatids facing opposite poles  Spindle is fully formed: Centrosomes are at opposite poles and spindle fibers are attached to kinetochores of chromosomes. Some spindle fibers attach to each other at the metaphase plate Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 18 4th ed., Chapter 4  Stages of mitosis: Anaphase  Sister chromatids are pulled apart by spindle fibers (microtubules).  Spindle fibers pull separated sister chromatids (= new ‘daughter chromosomes’) toward opposite poles (characteristic V shape) Figure 4.8d Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 19 4th ed., Chapter 4  Stages of mitosis: Telophase  Cytokinesis (= the splitting of the cell) starts  Nuclear envelope forms around each group of chromatids Nucleoli form again Spindle fibers come apart Chromosomes decondense to become chromatin again Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 20 4th ed., Chapter 4  Cytokinesis is the final stage of cell division Cytokinesis: Parent cells split into two daughter cells with identical nuclei Result: Each new daughter cell has a full set of daughter chromosomes (2n = diploid) that are identical to the parent cell Figure 4.8f Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 21 4th ed., Chapter 4  Mitosis: Once more Youtube video clips: https://www.youtube.com/watch?v=AhgRhXl7w_g https://www.youtube.com/watch?v=C6hn3sA0ip0 22 Cytokinesis: The cytoplasm divides and produces two daughter cells Animals have contractile ring that contracts to form cleavage furrow Plants cells have cell plate that forms near equator of cell Organelles (e.g. ribosomes, mitochondria, Golgi bodies) are distributed to each daughter cell Fig. 4.9 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 23 4th ed., Chapter 4 Mitosis: Once more Copyright © Campbell & Reece 24 Mitosis: Once more Copyright © Campbell & Reece 25 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 26 4th ed., Chapter 4  Overview of Meiosis  Two rounds of meiosis  Replication occurs once  Cells divide twice Fig. 4.12 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 27 4th ed., Chapter 4  Overview of Meiosis I  Homologs pair up, exchange parts, and then segregate  Maternal and paternal homologous pairs of chromosomes recombine and create new combinations of alleles (‘crossing- over’)  After recombination (crossing over), homologous pairs of chromosomes segregate to different daughter cells  Sister chromatids remain together throughout meiosis I  Depending on the species, length of time in prophase I can be short or very long Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 28 4th ed., Chapter 4  Prophase I: Homologous chromosomes pair up and are held together by synaptonemal complex Crossing-over (recombination) occurs during Prophase I Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., Feature Fig. 4.13 4th ed., Chapter 4 29  Prophase I (continued): Synaptonemal complex comes apart and chromatids in each tetrad become visible Feature Fig. 4.13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 30 4th ed., Chapter 4  In Metaphase I and Anaphase I, homologs move to opposite poles Note that the centromeres do not divide and sister chromatids are not separated Feature Fig. 4.13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 31 4th ed., Chapter 4 Meiosis I: from diploid (2n) to haploid (n) Feature Fig. 4.13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 32 4th ed., Chapter 4 During Meiosis II, sister chromatids separate and move to opposite poles Feature Fig. 4.13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 33 4th ed., Chapter 4 Meiosis II: from haploid (n) to haploid (n) Feature Fig. 4.13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 34 4th ed., Chapter 4 Meiosis: Once more 35 Meiosis: Once more 36  Meiosis clips https://www.youtube.com/watch?v=vyf2xwqzfFs https://www.youtube.com/watch?v=BVO-Ram1L2M https://www.youtube.com/watch?v=D1_-mQS_FZ0 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 37 4th ed., Chapter 4 38 Mitosis Meiosis Purpose: Produce somatic cells for growth or replacing other cells. Somatic cells undergo Purpose: Produce gametes (egg & meiosis sperm cells); germ cells undergo meiosis. 39  The cell cycle is a repeating pattern of cell growth and division  During mitosis chromosomes are equally distributed to two genetically identical daughter cells  Interphase: 3 parts: gap 1 (G1) phase, synthesis (S) phase, gap 2 (G2) phase Period of cell growth and chromosome duplication between divisions Formation of microtubules in cytoplasm  Centrosome – microtubule organizing center near the nuclear envelope (pair of centrioles in animal cells)  Centrioles – core of centrosome, not found in plant cells Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 40 4th ed., Chapter 4  The cell cycle: An alternation between interphase and mitosis  G1 and G2 phases: Most of cell growth occurs during these phases  Some terminally differentiated cells stop dividing and arrest (stop) in G0 stage  S Phase: DNA replication occurs. This result in two identical sister chromatids in later stages. Fig. 4.7a Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 41 4th ed., Chapter 4  Checkpoints help regulate the cell cycle  At each checkpoint, prior events must be completed before the next step of the cycle can begin  Details of cell-cycle regulation and checkpoint controls are described in Chapter 17 Fig. 4.11 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 42 4th ed., Chapter 4  Two general types of cells in plants and animals  Somatic cells make up vast majority of cells in the organism In G0 or are actively going through mitosis  Germ cells are precursors to gametes Set aside from somatic cells during embryogenesis Become incorporated into reproductive organs Only cells that undergo meiosis produce haploid gametes 43 Down-Syndrome: Mistake during Meiosis Trisomy 21: The cause for down-syndrome Probability with mother’s age: 25: 1/1200 35: 1/350 40: 1/100 49: 1/10 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 44 4th ed., Chapter 4  Mistakes in meiosis produce defective gametes Nondisjunction – mistakes in chromosome segregation during Meiosis I or II (usually during Anaphase I, e.g. trisomy 21) May result in gametes or embryos that don’t survive Can also result in abnormal chromosome numbers in surviving individuals (e.g. trisomy 21, Down syndrome; or XXY, Klinefelter syndrome) Many hybrids between species (i.e. donkey x horse  mule) are sterile because chromosomes cannot pair properly (hybrid sterility, see Figure 4.15) Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 45 4th ed., Chapter 4 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 46 4th ed., Chapter 4  Meiosis contributes to genetic diversity in two ways  Crossing-over between homologs creates different combinations of alleles within each chromosome  Independent assortment of non-homologs creates different combinations of alleles Fig. 4.16 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 47 4th ed., Chapter 4  Independent assortment A a A a B b b B A a A a B b b B A A a a A A a a B B b b b b B Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4th ed., Chapter 4 B 48  Gametogenesis in sexually reproducing animals  Germ line – specialized diploid cells set aside during embryogenesis  Gametogenesis – the formation of gametes Involves meiosis as well as specialized events before and after meiosis Different types of animals have variations on general aspects of this process In humans, oogenesis produces one ovum from each primary oocyte In humans, spermatogenesis produces four sperm from each primary spermatocyte Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 49 4th ed., Chapter 4