Chapter 2 GBBE Part III Cell Division by Meiosis : The Basis of Sex

1. Chapter 2 GBBE Part III Cell Division by Meiosis: The Basis of Sex • Objections of this Section: • Meiosis vs. Mitosis Comparison • Male and Female Reproductive Systems • Role of Mitosis and Meiosis in Sexual Life Cycles • Spermatogenesis and Oogenesis, the processes that form gametes. • Origins of Genetic Variation

2. 1. Why Sex? • A major question is why sexual reproduction persists when parthenogenesis appears in some ways to be a superior form of reproduction. Contemporary evolutionary thought proposes some explanations. It may be due to selection pressure on the clade (a group consisting of a species and all its descendants) itself —the ability for a population to radiate more rapidly in response to a changing environment through sexual recombination than parthenogenesis allows. Alternatively, sexual reproduction may allow for the “racheting” of evolutionary speed as one clade competes with another for a limited resource.

3. Parthenogenesis: http://www.pbs.org/wgbh/nova/body/alternative-cloning.html http://en.wikipedia.org/wiki/Parthenogenesis

4. Cladogram (family tree) of a biological group. The red and blue boxes represent clades (i.e., complete branches).

6. 2. Distinguish Between Asexual and Sexual Reproduction Asexual Reproduction Sexual Reproduction The creation of a new organism by combining the genetic material of two organisms. The two main processes are: Meiosis - involving the halving of the number of chromosomes; and Fertilization- involving the fusion of two gametes and the restoration of the original number of chromosomes. • A mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only. Examples include: • Binary fission in bacteria • Mitosis used in the growth and development of multi-cellular organisms • budding in yeast cells • vegetatative propagation in plants

7. 3. Comparison of Mitosis and Meiosis Mitosis/ Meiosis Comparison Table

8. 4. Compare the end products that are produced at the end of meiosis I and meiosis II.Are the cells at the end of meiosis I haploid or diploid?How about the cells at the end of meiosis II?

9. Overview of meiosis: reduction in chromosome number 2n 4n 2n 4n n chromosomes Replication chromatids MEIOSIS I & II chromosomes (4 cells) n

10. Human Life Cycle (simplified!) n n 2n 2n Meiosis Fertilization DIPLOID 46 HAPLOID 23 DIPLOID 46

11. The Human Life Cycle • Meiosis reduces the chromosome number of the cells that are produced. Diploid(2N) cells become haploid(1N) cells. Meiosis produces new combinations of genes by: • Random assortmentof paternal and maternal chromosomes • Recombination- the exchange of chromosome parts between chromatids. • Fertilization restores the • diploid condition by • combining two haploid(1N) • sets of chromosomes to make a diploid (2N) cell. • ( See Pg 34 Text)

12. 6. See the Hand Out of 3 different sexual life cycles… Animal Plants & some algae Fungi & some protists

13. Two Cell Types are found in Sexual Life Cycles 7. Somatic Cells are Diploid 8. Sex Cells are Haploid Reproductive cells having the haploid number of chromosomes, especially a sperm or egg capable of fusing with a gamete of the opposite sex to produce a fertilized egg. • A somatic cell is generally taken to mean any cell forming the body of an organism. • Internal organs skin, bones, blood and connective tissue are all made up of somatic cells. Is this human karyotype from a somatic cell or sex cell? How do you know ?

14. 9. Meiosis produces new combinations of genes in 3 ways. A. The 1st way that meiosis produces new combinations of genes is by Recombination or Crossing-over between chromosomes • The exchange of genetic material between homologous chromosomes is known as genetic recombination.

17. Crossing over

19. Chromosome Behavior and Gene Linkage https://wikispaces.psu.edu/display/Biol110Sum/Chromosome+Behavior+and+Gene+Linkage

20. B. The 2nd way is through: Independent Assortment or Random Assortment of chromosomes i. Different combinations of maternal and paternal chromosomes end up in the sex cells. ii. This occurs because each homologous pair of chromosomes is positioned independently of the other pairs at metaphase during meiosis I.

21. Independent assortment in meiosis I

22. The Independent assortment of chromosomes iii. The number of combinations possible when chromosomes assort independently into gametes is 2n, where n = haploid number of chromosomes iv. For humans (n = 23), there are 223 or about 8 million possible combinations of chromosomes

23. The Independent assortment of chromosomes If the # of different gamete diploid # of chromosomes is:the value of n is:combinations: 2n = 2 n=1 2 2n= 4 n=2 4 2n=6 n=3 8 2n= 8 n=4 16 2n =10 n=5 32 2n = 46 n=23 ?

24. Stages of Meiosis I also known as the “Reduction Division”. Why?

26. C. The 3rd way to add variation to sexually reproducing organisms is random Fertilization i. Only one sperm fertilizes an ovum ii. 8 million (223) different combinations of the 23 human chromosomes iii. So, a zygote results from one of about 70 trillion combinations of chromosomes • (8 million x 8 million) iv. Doesn’t include crossing-over or other sources of genetic variation

27. 10. Name and Discuss the 4 processes which add genetic variation to sexually reproducing organisms. • Independent assortment of chromosomes • Crossing-over between chromosomes • Random Fertilization • Mutation

28. Meiosis Animation • http://highered.mcgraw hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html (Meiosis Animation) • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__maturation_of_the_follicle_and_oocyte.html (Ovulation) • http://www.mayoclinic.com/health/ovulation/MM00108 (Ovaulation Animation) • http://www.youtube.com/watch?v=Cr8D5npEc0Q (Spermatogenesis) • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__spermatogenesis__quiz_1_.html

29. 11. Gametogenesis • Gametogenesis is the formation of mature ova (eggs) and spermatozoa. • In male the production of sperm occurs in the testis (seminiferous tubules). • In females the production of gametes takes place in the ovary.

30. The Male reproductive System

31. A. Spermatogenesis (48 days) 1. Process begins with a diploid stem cell called a spermatogonium, this cell divides mitotically, yielding two daughter cells. Only one becomes specialized into a mature sperm! 2. Spermatogonia accumulate cytoplasm and replicate DNA, becoming primary spermatocytes.

33. Sperm Formation

34. Sperm Formation continued … 3. During Meiosis I primary spermatocyte divides from two equal-sized haploid cells called secondary spermatocytes. 4. In meiosis II each secondary spermatocyte divides to yield two equal-sized spermatids.

35. Cross section of Seminiferous Tubules

36. B. Female Reproductive System

37. rectouterine pouch (cul de sac ) Zen Seeker The Female Reproductive

38. B. Oogenesis 1. Female production of gametes takes place in the ovaries 2. Cells in the ovary, called oogonia, divide by mitosis and form primary oocytes that undergo meiosis. 3. During cytoplasmic cleavage in meiosis I one cell receives 95% of the cytoplasm and will become a secondary oocyte.

39. Oogenesis continued… 4. In the second mitotic division, the same disproportionate cleavage results in one cell retaining most of the cytoplasm; the large cell is called ootid. 5. Ootid is the functional gamete and the smaller cells are known as polar bodies.

40. Oogenesis

41. Oogenesis

42. Secondary Oocyte and Polar Body

43. Comparing Duration of Meiosis