1. MEIOSIS

2. Meiosis cell division gametes, half chromosomes,The form of cell division by which gametes, with half the number of chromosomes, are produced. Diploid (2n)  haploid (n)Diploid (2n)  haploid (n) Meiosissexual reproduction.Meiosis is sexual reproduction. Two divisionsmeiosis I meiosis IITwo divisions (meiosis I and meiosis II).

3. Meiosis Sex cells gametes (sperm or egg)Sex cells divide to produce gametes (sperm or egg). Gameteshalf chromosomesGametes have half the # of chromosomes. Occurs only in gonads (testes or ovaries).Occurs only in gonads (testes or ovaries).

4. Three sexual life cycles differing in the timing of meiosis and fertilization

5. Moss with Sporophytes Gametophytes

6. Meiosis 2n=4 sex cell diploid (2n) n=2 meiosis I n=2 sperm haploid (n) meiosis II

7. Spermatogenesis 2n=46 Spermato- cyte diploid (2n) n=23 meiosis I n=23 sperm haploid(n) meiosis II

8. Oogenesis 2n=46 Oocyte diploid (2n) n=23 meiosis I n=23 ovum haploid(n) meiosis II polarbodies

9. Interphase mitosisSimilar to mitosis interphase. Chromosomes(S phase).Chromosomes replicate (S phase). chromosome chromatids centromeresEach duplicated chromosome consists of two identical sister chromatids attached at their centromeres. CentrioleCentriole pairs also replicate.

10. Interphase NucleusnucleolusNucleus and nucleolus visible. nuclear membrane nucleolus cell membrane chromatin

11. Meiosis I (four phases) Cell division chromosomeone-half.Cell division that reduces the chromosome number by one-half. Four Phases Four Phases: a.prophase I b.metaphase I c.anaphase I d.telophase I

12. Prophase I Longest and most complex phase (90%).Longest and most complex phase (90%). ChromosomesChromosomes condense. Synapsis homologous chromosomes tetradSynapsis occurs: homologous chromosomes come together to form a tetrad.

13. Homologous Chromosomes chromosomesmaternal paternalPair of chromosomes (maternal and paternal) that are similar in shape and size. (tetrads)Homologous pairs (tetrads) carry genes controlling the same inherited traits. locus(position of a gene)Each locus (position of a gene) is in the same position on homologues. autosomes a.22 pairs of autosomes sex chromosomes b.01 pair of sex chromosomes

14. Homologous Chromosomes PaternalMaternal eye color locus eye color locus hair color locus hair color locus

15. Prophase I centrioles spindle fiber aster fibers

16. Prophase I - Synapsis Homologous chromosomes sister chromatids Tetrad

17. Crossing Over Crossing over (variation) chromatidsCrossing over (variation) may occur between nonsister chromatids. Crossing over chromatids chromatidCrossing over: segments of nonsister chromatids break and reattach to the other chromatid.

18. Crossing Over - variation nonsister chromatids site of crossing over variation Tetrad

20. Metaphase I equator OR equator

21. Metaphase I Shortest phaseShortest phase TetradsequatorTetrads align on the equator INDEPENDENT ASSORTMENT OCCURS: genes for different traitsINDEPENDENT ASSORTMENT OCCURS: genes for different traits sort independently of one another into gametes

22. Anaphase I

23. Homologous chromosomesHomologous chromosomes separate and move towards the poles. Sister chromatids centromeresSister chromatids remain attached at their centromeres.

24. Telophase I

25. haploid chromosomesEach pole now has haploid set of chromosomes. CytokinesisCytokinesis occurs and two haploid daughter cells are formed.

27. Meiosis II No interphaseNo interphase DNA replication (or very short - no more DNA replication) Remember: Meiosis II mitosis but the cells are different from each otherRemember: Meiosis II is similar to mitosis but the cells are different from each other

28. Prophase II prophasemitosissame as prophase in mitosis

29. Metaphase II metaphasemitosissame as metaphase in mitosis equator

30. Anaphase II anaphasemitosissame as anaphase in mitosis sister chromatids separatesister chromatids separate

31. Telophase II

32. telophasemitosisSame as telophase in mitosis. CytokinesisNuclei form. Cytokinesis occurs. Remember:four haploid daughter cells produced; 3 polar bodies and anRemember:four haploid daughter cells produced; 3 polar bodies and an egg in females, 4 sperm in males gametes = sperm or egg

35. Fertilization spermegg zygoteThe fusion of a sperm and egg to form a zygote - a fertilized egg n=23 egg sperm n=23 2n=46 zygote

36. Variation Important to population as the raw material for natural selection.Important to population as the raw material for natural selection. Question:Question: What are the three sexual sources of genetic variation?

37. Answer: 1. crossing over (prophase I) 2. independent assortment (metaphase I) 3. random fertilization Remember: variation is good !

38. The Results of Alternative Arrangements of Two Homologous Chromosome Pairs on the Metaphase Plate in Meiosis I

39. A Comparison of Mitosis and Meiosis

40. Question: 20 chromosomes (diploid) chromosomesA cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

41. Answer: 10 chromosomes (haploid)10 chromosomes (haploid)

42. Question: 40 chromatids chromosomesA cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

43. Answer: 10 chromosomes10 chromosomes

44. Question: In terms of Independent Assortment -how many different combinations of sperm could a human male produce ?In terms of Independent Assortment -how many different combinations of sperm could a human male produce ?

45. Answer Formula: 2 nFormula: 2 n Human chromosomes:2n = 46Human chromosomes:2n = 46 n = 23 n = 23 2 23 = ~8 million combinations2 23 = ~8 million combinations

46. 1) Three major differences between meiosis and the mitosis are:

47. 2) Compare the number of chromatids present in human cells before and after DNA replication occurs in interphase. 3) Compare and contrast oogenesis with spermatogenesis.

48. Determine the number of chromo- somes in a cell whose diploid (2n) number is 10 after: a. meiosis I b. meiosis II c. mitosis

49. What is the primary difference between sexual life cycles in animals when compared to fungi and plants?

50. Failure of chromosomes to separate properly during meiosis may result in a/an ____________ Disorder, such as Down Syndrome. Explain the evolutionary reason that Sickle Cell Anemia is more common among African Americans.

51. If you understand the process of meiosis then you know that: 1)It occurs only to make sex cells/gametes. 2) Four different cells are produced. 3) Crossing over (exchange among DNA of tetrads) occurs in Prophase I to make the cells genetically different. 4) The amount of DNA is reduced by half in Meiosis I.