F24_L_Mendel_MeiosisI PDF - Biology Lecture Notes

Remember … what are we trying to explain? http://biology.stackexchange.com/questions/34521/is-batesian-mimicry-more-important-for-females 1 Natural Selection - Five easy pieces Natural Selection 1) Variation 2) Heritable variation 3) Struggle ...

Remember … what are we trying to explain? http://biology.stackexchange.com/questions/34521/is-batesian-mimicry-more-important-for-females 1 Natural Selection - Five easy pieces Natural Selection 1) Variation 2) Heritable variation 3) Struggle 4) Differential reproduction based on heritable variation 5) Changes in heritable characteristics of the population - evolution as a necessary consequence 2 1  Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint Variation Heritable variation ? Struggle for existence Differential reproduction based on heritable variation Changes in characteristics of the population = EVOLUTION 3 Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint Darwin’s Dilemma No understanding of inheritance Blending inheritance the predominant view of his day A sensible view, but counter to Darwin’s theory  Would destroy variation 4 2  Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint 5 Darwin had a problem Hey! What happens to variation? What’s the Mendel had solutions big idea!!! Segregation Independent assortment Understanding the mechanics of meiosis necessary for understanding Mendel’s solutions And recombination 6 3  Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint Today:  Brief review of basic terms related to inheritance  Review of the mechanism of meiosis  Inheritance and breeding Upcoming meetings  Variation, Natural selection, and implications 7 Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint The solution Particulate inheritance Discovered by Gregor Mendel (1860s) Significance not appreciated by Darwin Or others until much later 8 4  Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint Basic terms Gene  Discrete unit of DNA (or RNA) Genes are on Chromosomes  Very long DNA molecules Locus  The location of the gene on the chromosome 9 Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint Basic terms Diploid (2n) individuals have two copies of each chromosome Called homologous pairs One from Mom, one from Dad E.g. Humans  23 pairs of homologous chromosomes 10 5  Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint 11 Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint Basic terms Diploid individuals have two copies of each gene One on each homologous chromosome Alternate forms of a gene are called alleles A diploid individual can have two different alleles 12 6  Mendel and Meiosis Why Mom and Dad aren’t like buckets of paint Fig. 13.2 13 Mitosis - IPMAT Makes two copies of the cell Growth, damage repair, etc. Review pp. 232-33 if necessary Five phases I- Interphase P - Prophase M - Metaphase A - Anaphase T - Telophase 12.5 14 7  Meiosis - The problem Sexual reproduction involves fusion of two gametes Ifthe gametes were diploid, the number of chromosomes would ______ every generation! 15 Meiosis - The problem Sexual reproduction involves fusion of two gametes Ifthe gametes were diploid, the number of chromosomes would double every generation! 16 8  Meiosis - The problem Sexual reproduction involves fusion of two gametes Ifthe gametes were diploid, the number of chromosomes would double every generation! Solution - Halve the number of chromosomes when forming haploid gametes (1n) via a process called meiosis Fusion of haploid gametes restores diploid number of chromosomes 17 Meiosis I - The process Similar to Mitosis, but … Produces four haploid (1n) daughter cells instead of two diploid daughter cells Daughter cells NOT identical!!! Fig. 13.6 18 9  Meiosis I - The process Similar to Mitosis, but … Produces four haploid (1n) daughter cells instead of two diploid daughter cells Daughter cells NOT identical!!! Five phases (Times 2: Meiosis I and II) IPMAT I IPMAT II 19 Meiosis I - The process Five phases (see Fig. 13.7) I - Interphase I  Chromosomes duplicate, forming identical sister chromatids joined at centromeres (=Mitosis) 20 10  Meiosis I - The process Five phases I- Interphase I P - Prophase I  Homologous chromosomes form pairs (called tetrads) 21 Meiosis I - The process Five phases I- Interphase I P - Prophase I M - Metaphase I  Homologous pairs line up at metaphase plate 22 11  Meiosis I - The process Five phases I- Interphase I P - Prophase I M - Metaphase I A - Anaphase I  Homologous chromosomes pulled apart 23 Meiosis I - The process Five phases I- Interphase I P - Prophase I M - Metaphase I A - Anaphase I T - Telophase I We now have two haploid cells, but … Each chromosome still has two sister chromatids 24 12  Meiosis II - The process Five phases I - Interphase II  May not be present. If so, no more duplication P - Prophase II  Chromosomes move towards metaphase plate 25 Meiosis II - The process Five phases M - Metaphase II  Chromosomes line up at metaphase plate A - Anaphase II  Sister chromatids pulled apart 26 13  Meiosis Result - Four Haploid gametes See Fig. 13.8 27 This cell is … A. Haploid B. Diploid 28 14  These two cells are both… A. Haploid B. Diploid 29 These two cells are the result of … A. Mitosis B. Meiosis I C. Meiosis II 30 15  How many chromosomes are there? A. 1 B. 2 C. 4 D. 8 31 How many chromatids are there? A. 1 B. 2 C. 4 D. 8 32 16  How many chromosomes are there? A. 1 B. 2 C. 4 D. 8 33 This diagram depicts … A. Meiosis I B. Meiosis II C. Neither 34 17  Suppose a plant with one allele for red flowers and one allele for white flowers has pink flowers. Mendel’s insight suggests … 1. Variation is not destroyed when dissimilar alleles meet. 2. Gametes from a pink flowered plant will have red or white alleles, but not pink alleles 3. Both 35 Meiosis Implications for diversity of gametes Segregation Fig. 14.7 36 18  Meiosis Implications for diversity of gametes Segregation No Blending! Thanks! 37 Meiosis Thanks Implications for again! diversity of gametes Segregation No Blending! See Fig. 14.8 Independent assortment 8.4 million possible combinations for humans!!! 38 19  Meiosis But wait …. there’s more!!! Recombination Fig. 13.11 39 Meiosis Implications for diversity of gametes Segregation No Blending! Now we’re talkin’! Independent assortment Recombination 40 20  Meiosis Implications for diversity of gametes Segregation Now we’re No Blending! talkin’! Independent assortment Recombination About 50 males in this room, each producing about 20 million sperm during lecture ->1 Billion sperm  All unique! 41 Summary Mitosis and Meiosis are very similar processes, however … Daughter cells in mitosis are ± identical Daughter cells in meiosis are not  Segregation, Independent asst., recombination Darwin’s dilemma regarding inheritance was largely solved by Mendel Variation is preserved by segregation Variety in gametes is created by Indep. Asst. Recombination adds still more variety 42 21