1. Sexual Reproduction and Genetics Chapter 10

2. 10.1: Meiosis MAIN IDEA: Meiosis produces haploid gametes.

3. In Our Body Cells: Each chromosome has a matching pair - homologous pairs One chromosome from each pair came from mother, other from father Homologous chromosomes - code for the same type of traits, but don’t have the exact same information

4. Human Chromosomes

5. Humans Have 23 pairs of chromosomes (46 total) Each chromosome has about 1500 genes Genetic info passed from parents to children in sexual reproduction

6. Types of Reproduction 1. Asexual Single parent Offspring- genetically identical to parent No sex cells 2. Sexual 2 parents Offspring - genetically different from parents – variation Involves sex cells

7. Body Cells vs. Sex Cells Body (somatic) cells Diploid - contain both chromosomes of each pair Represented by 2n Sex cells (gametes) Haploid - Contain half the number of chromosomes; only one of each pair Represented by n

8. Haploid and Diploid If corn body cells have 20 chromosomes, how many are in the gametes? If an organism has a haploid number of 18, what is the diploid number? n= 24. Is this the haploid or diploid? Is this the number of chromosomes in the gametes or body cells?

9. Meiosis Special type of cell division that forms gametes – occurs in reproductive parts Meiosis called reduction division – reduces # of chromosomes in half Fertilization – 2 gametes combine – zygote cells are diploid Sexual reproduction is a cycle

11. Meiosis Interphase (same as before) 2 divisions: Meiosis I Meiosis II How many cells will result? How many cells resulted from mitosis?

12. Phases of Meiosis Meiosis I Prophase I, metaphase I, anaphase I, telophase I Meiosis II Prophase II, metaphase II, anaphase II, telophase II

13. What happens in each phase?

14. Prophase I (like mitosis) Chromosomes become visible; sister chromatids join at centromeres Nuclear membrane disappears; Spindle fibers start to form

15. Prophase I (only meiosis) 2 matching homologous pairs (one from father, one from mother) join together – synapsis Crossing over occurs - piece of one chromosome is exchanged with piece of another

16. chromatid centromere

17. Crossing Over

18. Prophase I

19. Metaphase I Matching homologous pairs (tetrads) line up across equator of cell Line up randomly Spindle fibers attach to centromeres of homologous pairs

20. Anaphase I Each pair of matched chromosome from the homologous pairs move to opposite ends of the cell Reduced from 2n to n

21. Telophase I Matching pairs have moved to opposite ends; cytokinesis occurs to make 2 cells

22. After Meiosis I… Cells have half the number of chromosomes as original cell, but in matching pairs

23. DO NOW What is the end result of meiosis? Why is meiosis called a “reduction division”, and why is it important? What is a homologous pair of chromosomes? If a cell contains 54 chromosomes before meiosis, how many are in each cell after meiosis?

24. Meiosis II Similar to mitosis NOT another interphase Prophase II – chromosome pairs begin moving toward equator and spindle fibers form Metaphase II – chromosome pairs line up across equator; spindle fibers attach to each chromatid at centromere

25. Meiosis II Prophase II Metaphase II

26. Meiosis II cont’d Anaphase II – pairs of chromosomes are separated, and move along spindle toward poles of cell Telophase II – chromosomes are at opposite ends of cell, cytokinesis occurs After Meiosis II – 4 haploid daughter cells

27. Meiosis II cont’d Anaphase II Telophase II 4 cells

29. Answer the Following: How does the chromosome # change with each cycle of mitosis and fertilization? What must occur to keep the chromosome number constant when fertilization occurs?

30. DO NOW What is the end result of meiosis? What is a homologous chromosome pair? Why is it important that meiosis is a “reduction” division?

31. Genetic Variation During prophase I, crossing over can occur Because homologous pairs are randomly separated, different gametes are formed When chromosomes recombine during fertilization, new combination of chromosomes results

32. Genetic Variation

33. Checkpoint How is sexual reproduction an advantage to a species? Explain 2 reasons why you do not look exactly like either of your parents.