Meiosis

1. Meiosis Chapter 10

2. Meiosis: reduction divisionGametes (sperm, egg, pollen, ovule) go through division twice

3. Sexual Reproduction Chromosomes are duplicated in germ (sex) cells Germ cells are immature reproductive cells that develop in male and female animals (2n, diploid) Germ cells undergo meiosis and cytokinesis Gametes are mature (1n, haploid) germ cell descendents (sperm, egg, pollen, ovule) Gametes (sperm from dad and egg from mom) meet at fertilization and create a fertilized egg (zygote)

4. Asexual Reproduction Single parent produces offspring All offspring are genetically identical to one another and to parent Fungi (yeast) and bacteria Binary fission (budding)

5. Sexual Reproduction Involves Meiosis Gamete production Fertilization Produces genetic variation among offspring

6. Homologous Chromosomes Carry Different Alleles Cell has two of each chromosome One chromosome in each pair from mother, other from father Paternal and maternal chromosomes carry different alleles (genes, not jeans!)

7. Stepped ArtFigure 10.5Page 168

8. Sexual Reproduction Shuffles Alleles Through sexual reproduction, offspring inherit new combinations of alleles, which leads to variations in traits Crossing over (chiasma) in Prophase I (Meiosis I) This genetic variation is the basis for evolutionary change and the reason you do not look EXACTLY like any of your relatives

9. Gamete Formation Gametes are haploid cells (sperm, eggs, pollen, ovule) Arise from germ cells

10. Chromosome Number Sum total of chromosomes in a cell Germ cells are diploid (2n) Gametes are haploid (n) Meiosis halves chromosome number (from 2n to 1n)

11. Meiosis: Two Divisions Two consecutive nuclear divisions Meiosis I Meiosis II DNA is not duplicated between divisions Four haploid nuclei form

12. In-text figurePage 165

13. Stepped ArtFigure 9.1Page 152

14. Meiosis I

15. Meiosis II The two sister chromatids of each duplicated chromosome are separated from each other

16. Stepped ArtFigure 10.4(1)Page 166

17. Stepped ArtFigure 10.4(2)Page 167

18. Prophase I Each duplicated chromosome pairs with homologue Homologues swap segments (crossing over; chiasma) Each chromosome becomes attached to spindle

19. Metaphase I Chromosomes are pushed and pulled into the middle of cell The spindle is fully formed

20. Anaphase I Homologous chromosomes segregate The sister chromatids remain attached

21. Telophase I The chromosomes arrive at opposite poles Usually followed by cytoplasmic division

22. Prophase II Microtubules attach to the centromeres (aka kinetochores) of the duplicated chromosomes

23. Metaphase II Duplicated chromosomes line up at the spindle equator, midway between the poles

24. Anaphase II Sister chromatids separate to become independent

25. Telophase II The chromatids arrive at opposite ends of the cell A nuclear envelope forms around each set of chromatids RESULT: 4 haploid cells

26. Animation

27. Details of Crossing Over

28. Effect of Crossing Over After crossing over, each chromosome contains both maternal and paternal segments Creates new allele combinations in offspring (increased genetic variability)

29. Random Alignment During transition between Prophase I and Metaphase I, microtubules from spindle poles attach to centromeres of chromosomes Initial contacts between microtubules and chromosomes are random Random separation of homologous chromosomes is called independent assortment

30. Random Alignment Either the maternal or paternal member of a homologous pair can end up at either pole The chromosomes in a gamete are a mix of chromosomes (independent assortment; variation) from the two parents

31. Possible Chromosome Combinations As a result of random alignment, the number of possible combinations of chromosomes in a gamete is: 2n (n is number of chromosome types)

32. Possible ChromosomeCombinations23 = 8 variations

33. Animation

34. Plant Life Cycle

35. Animal Life Cycle

36. Oogenesis

37. Spermatogenesis

38. Fertilization Male and female gametes unite and nuclei fuse Fusion of two haploid nuclei produces diploid (2n) nucleus in the zygote Uniting of gametes is random (2n) Adds to variation among offspring

39. Factors Contributing to Variation among Offspring Crossing over during Prophase I Random alignment of chromosomes at Metaphase I Random combination of gametes at fertilization

40. Mitosis Functions Asexual reproduction Growth, repair Occurs in somatic cells Produces clones Two diploid (2n) cells produced Mitosis & Meiosis Compared Meiosis Function Sexual reproduction Occurs in germ cells Produces variable offspring Four haploid (1n) cells produced

41. Prophase vs. Prophase I Prophase (Mitosis) Homologous pairs do not interact with each other Prophase I (Meiosis) Homologous pairs become zippered together and crossing over occurs

42. Anaphase, Anaphase I, and Anaphase II Anaphase I (Meiosis) Homologous chromosomes separate from each other Anaphase/Anaphase II (Mitosis/Meiosis) Sister chromatids of a chromosome separate from each other

43. Results of Mitosis and Meiosis Mitosis Two diploid cells produced Each identical to parent Meiosis Four haploid cells produced Differ from parent and one another

44. Figure 10.11Page 174

45. Figure 10.10Page 172-173