© 2014 Pearson Education, Inc. AP Bio Homework: (next slide) 2.AP exam practice question 3.Notes session 4.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 ( ) on Chapter 9 Goals: Meiosis Continued

© 2014 Pearson Education, Inc. Due today: Mitosis & Meiosis Lab Bench activity Ongoing: Chapter 10 reading guide: due Mastering Biology Chapter 10 HW: due New: Meiosis POGIL & Human Gamete production ( ) Watch/take notes on Double Helix film (quiz on ) Watch/video guide on Bozeman Science video ( )

© 2014 Pearson Education, Inc. Figure 10.8 MEIOSIS I: Separates homologous chromosomes Prophase IMetaphase IAnaphase I Telophase I and Cytokinesis Prophase IIMetaphase IIAnaphase II Telophase II and Cytokinesis MEIOSIS II: Separates sister chromatids Sister chromatids Centromere (with kinetochore) Sister chromatids remain attached Centrosome (with centriole pair) Metaphase plate Chiasmata Spindle Cleavage furrow Homologous chromosomes separate Microtubule attached to kinetochore Fragments of nuclear envelope Homologous chromosomes Sister chromatids separate Haploid daughter cells forming

© 2014 Pearson Education, Inc. 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 Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I

© 2014 Pearson Education, Inc. Figure Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II

© 2014 Pearson Education, Inc. Figure Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1Combination 2Combination 3Combination 4

© 2014 Pearson Education, Inc. 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 Prophase I of meiosis Pair of homologs Nonsister chromatids held together during synapsis

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Chiasma Centromere TEM Synapsis and crossing over Nonsister chromatids held together during synapsis

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Chiasma Centromere TEM Anaphase I Synapsis and crossing over Breakdown of proteins holding sister chromatid arms together Nonsister chromatids held together during synapsis

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Chiasma Centromere TEM Anaphase I Synapsis and crossing over Breakdown of proteins holding sister chromatid arms together Anaphase II Nonsister chromatids held together during synapsis

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Chiasma Centromere TEM Anaphase I Synapsis and crossing over Breakdown of proteins holding sister chromatid arms together Anaphase II Daughter cells Recombinant chromosomes Nonsister chromatids held together during synapsis

© 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