1022020 Title Biology 11707 Objectives To review learning
10/2/2020 Title: Biology 1/17/07 Objectives: To review learning about genetic variation due to meiosis and about gametogenesis Class Topics • Hand in the W. S. Science skills before the bell rings – 2 A hand in p. 157 #16 and #18 • Chapter 7 Quiz 1 • Continue Chapter 7 – Genetic variation – Gametogenesis “I would rather fail in a cause that someday will triumph, than to win in a cause that I know will someday fail. ” Woodrow Wilson Friday, October 2, 2020 8: 35 AM 1
10/2/2020 Class Assignments What • • • Chapter 7 Quiz 1 1/17/07 W. S. Science Skills 1/17/07 2 A only – paragraphs from p. 157 (16 & 18) Meiosis W. S. 1/19/07 Chapter 7 Test 1/23/07 By When 1/17/07 • Due this class period • Due next class period • Due in the future 2
10/2/2020 Grade Sheet 3
10/2/2020 Postquiz Activities • Reread 144 -149 • Review – Independent assortment – Crossing over – Random mating 4
10/2/2020 Genetic variation • Allows for new genetic combinations – Unlike mitosis • 1. Independent assortment – Random distribution of homologous chromosomes • Each of the 23 pairs segregates independently – 223 combinations (8, 388, 608) from one cell 5
10/2/2020 Genetic variation (cont. ) • 2. Crossing-over – Occurs during Prophase I when homologous chromosomes synapse – Trading of genetic material between homologous chromosomes (switching genes) – Increases genetic diversity 6
10/2/2020 Genetic variation (cont. ) • 3. Random fertilization – Random fertilization means each gamete was independently assorted • (223 * 223) = 70, 368, 744, 177, 664 combinations 7
10/2/2020 Importance of genetic variation • Very important for evolution – change in characteristics of a population from one generation to the next • The pace of evolution can be sped up by increased genetic variation – Depends on natural selection 8
10/2/2020 Crossing Over • Video Clips – Items to note • Another name for crossing over? • In mitosis? – Why or why not? • How often? – Large chromosomes – Small chromosomes • What if crossing over doesn’t occur? 9
10/2/2020 Venn Diagram • Homologous chromosomes • somatic cells • gametes • 1 division • tetrads • cytokinesis • chromatids • Synapsis • unpaired chromosomes • diploid cells • crossing over • 2 divisions • haploid cells • ovum 10
10/2/2020 Meiosis and Gamete Formation • Spermatogenesis – – – Formation of sperm in the testes Primary spermatocytes (2 n) Secondary spermatocytes (n) Spermatids (n) Sperm (n) 4 haploid cells from one germ cell 11
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10/2/2020 Oogenesis • • Primary Oocyte (2 n) Secondary Ooctye, Polar Body (n) 1 Ootid, Polar bodies (n) 1 Ovum (n) 14
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10/2/2020 Sperm vs Ovum • Sperm – size - small – moves by flagellum – millions made per day – no food – produced in testes • Ovum – size - very large – no movement – fixed number • all made by 3 rd month of development – Yolk (amnion) supplies food – Ovaries 18
10/2/2020 Meiosis W. S. • Front side (Meiosis) – Guinea pig 2 n = 64 • Back side (Meiosis & Fertilization) – do not fill in the blanks on the right (fertilization side) – Do not use 4 different colors, two will suffice – Step 1 should be metaphase I – Step 3 should be both telophase I and prophase II 19
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