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AP Bio 02.04.16 Goals: Meiosis Continued 1. 2. 3. 4. Homework: (next slide) AP exam practice question Notes session Work on: Activity 46.1 Production of human gametes Regular book Chapters 32, 36 Old Book Chapters 45 & 46 FRQ & grid in quiz next week (02.11.16) on Chapter 9 © 2014 Pearson Education, Inc. Due today: • Mitosis & Meiosis Lab Bench activity Ongoing: • Chapter 10 reading guide: due 02.08.16 • Mastering Biology Chapter 10 HW: due 02.08.16 New: • Meiosis POGIL & Human Gamete production (02.08.16) • Watch/take notes on Double Helix film (quiz on 02.08.16) • Watch/video guide on Bozeman Science video (02.08.16) © 2014 Pearson Education, Inc. Figure 10.8 MEIOSIS I: Separates homologous chromosomes Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis MEIOSIS II: Separates sister chromatids Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Sister chromatids Centromere (with kinetochore) Sister chromatids remain attached Centrosome (with centriole Cleavage pair) furrow Chiasmata Metaphase Spindle plate Sister chromatids separate Homologous chromosomes separate Fragments of nuclear envelope Homologous chromosomes Microtubule attached to kinetochore © 2014 Pearson Education, Inc. Haploid daughter cells forming Genetic variation produced in sexual life cycles contributes to evolution • Mutations: – changes in an organism’s DNA – the original source of genetic diversity – create different versions of genes called alleles – Reshuffling of alleles during sexual reproduction produces genetic variation © 2014 Pearson Education, Inc. Origins of Genetic Variation Among Offspring • Three mechanisms contribute to genetic variation – Independent assortment of chromosomes – Crossing over – Random fertilization © 2014 Pearson Education, Inc. Independent Assortment of Chromosomes • Homologous pairs of chromosomes orient randomly at metaphase I of meiosis • In independent assortment, each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs © 2014 Pearson Education, Inc. Figure 10.10-1 Possibility 2 Possibility 1 Two equally probable arrangements of chromosomes at metaphase I © 2014 Pearson Education, Inc. Figure 10.10-2 Possibility 2 Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Metaphase II © 2014 Pearson Education, Inc. Figure 10.10-3 Possibility 2 Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2 © 2014 Pearson Education, Inc. Combination 3 Combination 4 Crossing Over • Produces recombinant chromosomes, which combine DNA inherited from each parent • Crossing over begins very early in prophase I, as homologous chromosomes pair up gene by gene • Formation of chiasmata © 2014 Pearson Education, Inc. Figure 10.11-1 Prophase I of meiosis Pair of homologs © 2014 Pearson Education, Inc. Nonsister chromatids held together during synapsis Figure 10.11-2 Prophase I of meiosis Pair of homologs Chiasma Centromere TEM © 2014 Pearson Education, Inc. Nonsister chromatids held together during synapsis Synapsis and crossing over Figure 10.11-3 Prophase I of meiosis Pair of homologs Chiasma Nonsister chromatids held together during synapsis Synapsis and crossing over Centromere TEM Anaphase I © 2014 Pearson Education, Inc. Breakdown of proteins holding sister chromatid arms together Figure 10.11-4 Prophase I of meiosis Pair of homologs Chiasma Nonsister chromatids held together during synapsis Synapsis and crossing over Centromere TEM Anaphase I Anaphase II © 2014 Pearson Education, Inc. Breakdown of proteins holding sister chromatid arms together Figure 10.11-5 Prophase I of meiosis Pair of homologs Chiasma Nonsister chromatids held together during synapsis Synapsis and crossing over Centromere TEM Anaphase I Breakdown of proteins holding sister chromatid arms together Anaphase II Daughter cells Recombinant chromosomes © 2014 Pearson Education, Inc. Random Fertilization • Random fertilization adds to genetic variation because any sperm can fuse with any ovum • The fusion of two human gametes = a zygote with any of about 70 trillion diploid combinations! ….... And that doesn’t even account for crossing over => every zygote is unique © 2014 Pearson Education, Inc. The Evolutionary Significance of Genetic Variation Within Populations • Enables Descent with modification: 1. Natural selection (non-random) 2. Variability of traits (random) 3. Over-production of offspring 4. Competition The result is organisms well-suited for their environments © 2014 Pearson Education, Inc.