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P10-Lecture 5- Mendel & Meiosis- Feb. 3

P10-Lecture 5- Mendel & Meiosis- Feb. 3 - Mendel...

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Unformatted text preview: Mendel and Meiosis Some Comments on Lab this week s Read over the whole module x You need to integrate/synthesize!!! x Know the Big Picture!! s You will be verifying the premises of Natural Selection for wing presence/absence ... s ...to reach a conclusion to the following question: x Did selection lead to evolution in this population? Natural Selection - Five premises s Natural Selection x1) Variation x2) Heritable variation x3) Struggle x4) Differential reproduction based on heritable variation x5) Changes in heritable characteristics of the population - evolution as a necessary consequence Mendel and Meiosis s Variation s Heritable variation s Struggle s Differential reproduction based on heritable variation ? s Changes in heritable characteristics of the population = EVOLUTION as a consequence. Mendel and Meiosis s Darwin's Dilemma x No understanding of inheritance x Blending inheritance the predominant view of his day x A sensible view, but counter to Darwin's theory 3Would destroy variation Mendel and Meiosis Why Mom and Dad aren't like buckets of paint s The solution xParticulate inheritance xDiscovered by Gregor Mendel (1860s) x Significance not appreciated by Darwin (or others) until much later s Darwin had a problem x What happens to variation? s Mendel had solutions: x Segregation x Independent assortment s Understanding the mechanics of meiosis necessary for understanding Mendel's solutions x And recombination Mendel and Meiosis Why Mom and Dad aren't like buckets of paint s Today: x Review of basic terms related to inheritance x Review of mitosis x Review of the mechanism of meiosis s Friday x Inheritance and breeding Mendel and Meiosis s Basic terms: See Fig. 12.9A x Gene unit of DNA (or RNA) x Genes are on Chromosomes 3 Very long DNA molecules x Allele: x Locus 3 The 3 Discrete alternative versions of a gene location of the gene on the chromosome Mendel and Meiosis s Basic terms: x Diploid individuals have two copies of each chromosome x Called homologous pairs x One from Mom, one from Dad x E.g. Humans 3 23 pairs of homologous chromosomes Mendel and Meiosis s A diploid individual can have two different alleles Cell Division Each DNA molecule with its attached proteins, is a chromosome. Each chromosome is duplicated as cell prepares for mitosis. = 2 DNA molecules attached together called sister chromatids. Mitosis occurs in the somatic cells (body cells). Human somatic cells = 46 total chromosomes or 23 pair. They are diploid or 2n. Diploid cells have 2 of each type of chromosome. Tetraploid? Polyploid? Mitosis maintains the chromosome number of the species through all the divisions of development, growth and repair. Mitosis s Division of nucleus mitosis s Division of cytoplasm - cytokinesis s Makes two copies of the cell x Growth, damage repair, etc. 2n 2n Look over Figs. 11.6 11.7 for mitosis Mitosis: IPMAT s Five phases: 1. Non-dividing cell replicatechromatin - I Interphase: 3 Centrosomes 2 pair centrioles (animal cells) 3 Chromatin condenses 3 Chromosomes duplicate, forming identical sister chromatids joined at s Five phases x P 2. Mitosis - IPMAT x I - Interphase Prophase (ignore prometaphase) x Nucleolus disappears x Nuclear envelope breaks apart x Spindle begins to assemble at poles of the cell x Kinetochores appear on sides of centromeres x Chromatids condense Mitosis - IPMAT s Five phases x I - Interphase x P - Prophase x M 3. Metaphase aster 3 Kinetochores attached to spindle fibers 3 Sister chromatids line up at metaphase plate at the center of spindle Metaphase showing spindle s Five phases Mitosis - IPMAT x I - Interphase x P - Prophase x M - Metaphase x A 4. Anaphase 3 Chromatids pulled apart to the poles of the cell by the spindle fibers at the centromere. 3 Sister chromatids are now called daughter chromosomes. s Five phases x Mitosis - IPMAT I Interphase; P Prophase; M Metaphase; A - Anaphase x T 5. Telophase x the new daughter nuclei & nuclear envelopes start to reform & the chromosomes uncoil. 3 Spindle disappears 3 Nucleolus appears 3 Cytokinesis Cleavage furrow- animals Cell plate- plants See Figs. 11.9-11.10 See Figure 11.9 Mitosis - IPMAT Figure 11.15 Meiosis - The problem s Sexual reproduction involves fusion of two gametes: x If the gametes were diploid, the number of chromosomes would double every generation! s Solution - Halve the number of chromosomes when forming gametes (1n) via a process called meiosis. x Fusion of haploid gametes restores diploid number of chromosomes. n + n 2n (zygote) (gametes) s Reduction division x Cells produced Meiosis have number of chromosomes as parent cell s Involves 2 successive nuclear divisions s Creates genetic variation. s Sexual reproduction is the basis for evolutionary change = diversity. e.g., Which children belong to each couple? Each has 2 children. 1 2 2 3 4 46 Human Mitosis -46 chromosomes -23 pair -2n (diploid) 46 46 46 46 46 46 2 divisions: Meiosis I Meiosis II 46 Unduplicated chromosomes Chromosomes replicate = chromatids 23 46 23 Meiosis In (haploid) Meiosis II 23 23 23 23 sister Results in 4 haploid daughter cells (i.e., chromatids eggs & sperm) separate Meiosis I - The process s Produces four haploid (1n) daughter cells instead of two diploid daughter cells as in mitosis s Meiosis I and II x Interphase I- occurs at start of meiosis See Figs. 12.2- 12.4 for meiosis Meiosis I - The process s Interphase I 3Chromosomes duplicate, forming 2 identical sister chromatids joined at centromeres (=Mitosis) 3In animals, centrioles have also duplicated Meiosis I - The process s Prophase I x Synapsis occurs x Homologous chromosomes form pairs (called tetrads) x Crossing over occurs= exchange of genetic information between nonsister chromatids (tetrads) 3 Form chiasmata Meiosis I - The process s Metaphase I x Homologous pairs (tetrads) line up at metaphase plate Meiosis I - The process s Anaphase I x Homologous chromosomes separate and are moved to opposite poles x Sister chromatids remain attached Meiosis I - The process s Telophase I s We now have two haploid cells, but ... x Each chromosome still has two sister chromatids s Five phases 3 May Meiosis II - The process x I - Interphase II not be present. If so, no more DNA duplication move towards metaphase plate x P - Prophase II 3 Chromosomes Meiosis II - The process s Five phases x M - Metaphase II 3 Chromosomes line up at metaphase plate x A- Anaphase II 3 Sister chromatids pulled apart x T Telophase II 3 Nuclei form 3 Cytokinesis occurs s Meiosis Result - Four Haploid gametes 12.5 Meiosis s Implications for diversity of gametes x1. No Blending x2. Segregation ...
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