Bioc270-02 Lecture Chapter 2 Cell Cycle Mitosis Meiosis PDF

General Genetics BIOL 270 Lecture Chapter 2 Dr Haslina Razali Fall 2024 PART I Basic Principles: How Traits Are Transmitted CHAPTER CHAPTER...

General Genetics BIOL 270 Lecture Chapter 2 Dr Haslina Razali Fall 2024 PART I Basic Principles: How Traits Are Transmitted CHAPTER CHAPTER 3 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 2 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 on 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 3 Hartwell et al., 4th ed., Chapter 4  Evidence that genes reside in chromosomes Mitosis – process that generates _______________containing 2 daughter cells 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. ❑ For instance, in humans: 46 chromosomes 46 chromosomes (parent cell) (each daughter cell) 4  Evidence that genes reside in chromosomes ❑ Meiosis – process that generates gametes (= egg and sperm cell ) that have ____the half 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 5 Hartwell et al., 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  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 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 8 Hartwell et al., 4th ed., Chapter 4 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 9  Homologous chromosomes are matched in size, shape and banding patterns ❑ Karyotype – micrograph (photo) of stained chromosomes arranged in homologous pairs (see Figure) 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 10  Karyotype of a human male ❑ The chromosomes most 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 11 Hartwell et al., 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 12 Hartwell et al., 4th ed., Chapter 4 Mechanisms of sex determination differ between species Homogametic vs Heterogametic 13 Table 4.2  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: o gap 1 (G1) phase, o synthesis (S) phase, o gap 2 (G2) phase ▪ Period of cell growth and chromosome duplication between divisions ▪ Formation of microtubules in cytoplasm o Centrosome – microtubule organizing center near the nuclear envelope (pair of centrioles in animal cells) o Centrioles – core of centrosome, not found in plant cells 14 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 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 15  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 duplication occurs. This result in two identical sister chromatids in later stages. G1 S G2 Fig. 4.7a Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 16 Hartwell et al., 4th ed., Chapter 4  What happens during interphase and checkpoints? ❑ Start of Interphase → G1 phase → the cell grows and protein necessary for cell division are synthesized. ❑ Enzymes necessary for DNA duplication ❑ G1/S checkpoint → cell is committed to divide ❑ S phase (DNA synthesis) → chromosome duplication (double) → production of identical sister chromatids joined at the centromere ❑ If this phase is blocked (by drugs or mutation) → Is there DNA duplication or mitosis? NO ❑ G2 phase → additional biochemical events necessary for cell division take place ❑ After G2/M checkpoint has passed, the cell is ready to divide ❑ Interphase → chromosomes are in relaxed (uncoiled and cannot be seen with a microscope) 17  What happens during interphase and checkpoints? ❑ Formation of microtubules in cytoplasm o Centrosome – microtubule organizing center near the nuclear envelope (pair of centrioles in animal cells) o Centrioles – core of centrosome, not found in plant cells ❑S and G2 stages → centrosomes replicate → 2 centrosomes at close proximity 18  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 Cell cycle: Interphase & Mitotic phase (Mitosis & Cytokinesis) Prometaphase https://www.thoughtco.com/stages-of-mitosis-373534 20  Mitosis Sister Two daughter chromatids cells separate 21  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 22 Hartwell et al., 4th ed., Chapter 4  Stages of Mitosis: Prometaphase ❑ Nuclear envelope breaks down, nucleus comes apart ❑ Spindle fibers (microtubules) extend from centrosomes and connect to kinetochores at centromere region of each chromatid. ❑ Mitotic spindle starts to forms (Kinetochore microtubules, polar microtubules & astral microtubules) ❑ Centrosomes are at or near opposite poles Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 23 Hartwell et al., 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 24 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4th ed., Chapter 4  Stages of mitosis: Anaphase ❑ Sister chromatids are pulled apart by spindle fibers (microtubules). ❑ Spindle fibers (kinetochore microtubles) pull separated sister chromatids (= new ‘daughter chromosomes’) toward opposite poles (characteristic V shape) Figure 4.8d Is the genetic information from one sister chromatids the same of it’s counterpart moving in the Copyright © The opposite direction? McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4th ed., Chapter 4 YES 25  Stages of mitosis: Telophase ❑ Cytokinesis (= the splitting of the cell) starts ❑ Nuclear envelope forms around each group of chromatids o Nucleoli form again o Spindle fibers come apart o Chromosomes decondense to become chromatin again 26  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 ❑ Large number of important organelles and cellular components (e.g. ribosomes, mitochondria, Golgi bodies, chloroplast) parceled out to emerging daughter cells (unequal distribution) Figure 4.8f 27 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 28 Hartwell et al., 4th ed., Chapter 4  After cell division ❑ Enters the Interphase ❑ G1 – Protein synthesis & cell growth ❑ S – Chromosome & centrosome duplication ❑ G2 – More protein synthesis & cell growth 29 Counting Chromosomes and DNA Molecules 30  Mitosis: Once more Youtube video clips: https://www.youtube.com/watch?v=AhgRhXl7w_g https://www.youtube.com/watch?v=C6hn3sA0ip0 31 Checkpoints help regulate the cell cycle ❑ At each checkpoint, prior events must be completed before the next step of the cycle can begin ❑ Chromosomes completely copied ❑ All kinetochore attached to spindle fibers before separating at centromeres ❑ Cell size sufficient Fig. 4.11 32  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 MITOSIS 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 33 Hartwell et al., 4th ed., Chapter 4  Genetic consequences of the cell cycle ❑ From one single cell to two daughter cells containing the same genetic materials. ❑ Each of the cells = full complement of chromosomes. ❑ BUT cytoplasmic content (organelles) are not identical or are evenly divided. Dr. Haslina Razali 34 Mitosis: Once more 35 Mitosis: Once more 36  Recap A. C. The three cells shown in figures a–c are all from the same individual. o For each cell, indicate what stage of cell division is represented? B. o State the number of chromosome and number of chromatids in each cell. 37  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 38 Hartwell et al., 4th ed., Chapter 4 Two types of division in Meiosis Reductional division Equational division 39  Prophase I: ❑ Homologous chromosomes pair up and are held together by synaptonemal complex ❑ Crossing-over (recombination) occurs during Prophase I Synapsed chromosome pair = bivalent (2 chromosomes)/tetrad (4 chromatids) What is crossing over? Crossing over is where genetic information is exchanged between nonsister chromatids of a homolog pair Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Feature Fig. 4.13 Hartwell et al., 4th ed., Chapter 4 40  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 41 Hartwell et al., 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 42 Hartwell et al., 4th ed., Chapter 4 Meiosis I: from diploid (2n) to haploid (n) ❑Interkinesis = No chromosome duplicate Feature Fig. 4.13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 43 Hartwell et al., 4th ed., Chapter 4  During Meiosis II, sister chromatids separate and move to opposite poles Are the sister chromatids identical to each other? NO Feature Fig. 4.13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 44 Hartwell et al., 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 45 Hartwell et al., 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 (Propose I – Pachytene) ▪ Sister chromatids remain together throughout meiosis I ▪ Depending on the species, length of time in prophase I can be short or very long ▪ Number of chromosome is reduced to half (haploid) Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 46 Hartwell et al., 4th ed., Chapter 4  Overview of Meiosis II ▪ Enters interkinesis, a period between Meiosis I and Meiosis II – No DNA duplication ▪ Separation of sister chromatids ▪ Number of chromosome is still half (Haploid) Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4th ed., Chapter 4 47 Meiosis: Once more 48 Meiosis: Once more 49  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., 4th ed., Chapter 4 50 Mitosis Meiosis Somatic cells undergo mitosis. Germ cells undergo meiosis. Purpose: Produce somatic cells for Purpose: Produce gametes (egg & growth or replacing other cells. sperm cells); 51 52  Mitosis versus Meiosis Table 4.3 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 53 Hartwell et al., 4th ed., Chapter 4 Mitosis versus Meiosis (continued) Table 4.3 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 54 Hartwell et al., 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 55 Hartwell et al., 4th ed., Chapter 4  Crossing over ❑Crossing-over between homologs creates different combinations of alleles within each chromosome 56  Independent assortment A a A a ❑ Independent B b b B assortment of non-homologs creates different A a A a combinations of alleles B b b B A A a a A A a a B 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  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 58 Hartwell et al., 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) Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 59 Hartwell et al., 4th ed., Chapter 4  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., 4th ed., Chapter 4 60 Klinefelter Syndrome: Mistake during meiosis ❑ extra X chromosome in a male ❑ Two X chromosomes -> female development fail ❑ Tall, thin and sterile, mental retardation Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4th ed., Chapter 4 61  Sterile hybrids Many hybrids between species (i.e. donkey (62) x horse (64) → mule (63)) are sterile because chromosomes cannot pair properly (hybrid sterility) Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4th ed., Chapter 4 62  https://www.denverpost.co m/2013/08/16/colorado- miracle-mule-foal-lived- short-life-but-was-well- loved/ Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Hartwell et al., 4th ed., Chapter 4 63