Mendel and Meiosis

1. Mendel and Meiosis Chp 10 Pp. 252-279

2. Contents • 10-2 Meiosis • 10-1 Mendel

3. Chromosome • Rod shaped structures made of DNA and proteins • Carrier of genetic material • Located in the nucleus • Copied and passed from generation to generation

5. Chromosomes • Sex chromosomes: chromosomes that determine the sex of an organism • Humans X and Y • Females: X X • Males: X Y Autosomes: all other types of chromosomes

6. Chromosomes

7. Homologous Chromosomes • 2 copies of each autosome • Same size and shape • Carry genes for the same trait • Ex. If 1 homologous chromosome contains gene for eye color the other homologous chromosome will too.

8. Homologous Chromosomes

9. Diploid Cell • Cell with 2 sets of chromosomes • Contains chromosomes for each homologous pair • Somatic Cells= Body Cells: Diploid • All human cells except sex cells are diploid. • One from each parent • 2n • Humans 2n = 46

10. Haploid • Cell containing one of each kind of chromosome • Sperm and egg cells = Gametes • 1 set of chromosomes • Half the number of chromosomes of diploid • n • Sperm + Egg = Zygote • n + n = 2n

11. Mitosis vs. Meiosis • Mitosis: t = two: Diploid 2n=46 • Meiosis: o = one: Haploid • n = 23

12. Meiosis • Gametes are produced in specialized body cells • Produces Sperm and Egg Cells • 2 divisions: Meiosis I and Meiosis II • Meiosis occurs in sex cells, not body cells • Results in 4 daughter cells • Each cell has half the chromosomes of the parent

13. Meiosis I • Interphase occurs: the cell grows and DNA replicates • Meiosis I begins • Original cell produces two new cells

14. Prophase I • DNA Coils tightly into chromosomes • spindle fibers appear • Each chromosome lines up next to the homologue • Synapis occurs: pairing of homologous chromosomes • Tetrad: Each pair of homologous chromosomes

15. Crossing Over • Crossing Over: why we do not look exactly like our parents. • Portions of the chromatid breaks off and attaches to adjacent chromatids on the homologous chromosome • Permits the exchange of genetic material between maternal and paternal chromosomes • Occurs during Prophase

17. Genetic Recombination • Crossing over produces a new mixture of genetic material • Occurs during Prophase

18. Causes of Variation • Chromosomes are assorted randomly • Crossing over may occur • Cells do not have identical genetic info as each other or the parent • Good: more chance of survival and evolution • Bad: mistakes more likely

19. Metaphase I • Tetrads line up randomly along the mid-line • Spindle fibers attach to centromeres

20. Anaphase I • Homologous chromosomes move to the opposite poles • Random separation or Independent Assortment results in separation of maternal and paternal chromosomes.

21. Telophase I • Chromosomes reach opposite ends of cell • Cytokinesis begins • cell is haploid

22. Meiosis II • Occurs in each cell formed in Meiosis I • Interphase does not occur again

23. Prophase II • Spindle fibers form and move the chromosomes to the mid-line of the dividing cell

24. Metaphase II • Chromosomes move to the mid-line of the dividing cell facing opposite poles of the dividing cell

25. Anaphase II • Chromatids separate and move to opposite poles of the cell

26. Telophase II • Nuclear membrane forms around the chromosomes in each of 4 new cells

27. Cytokinesis II • Cytoplasm divides • Cell Membrane closes off

28. End Result: • Four new cells that contain half of the original cells number of chromosomes • 4 sex cells are created

29. Meiosis Animation • Meiosis Animation

31. Haploid = one of each kind Diploid = two of each kind • 2n = diploid n = haploid

32. 23 23 WHY DO WE NEED HAPLOID? • EGG Female gamete Male gamete SPERM

33. Fertilization restores the diploid number 1n meiosis 1n fertilization 2n 2n Mitosis and cell growth 2n

34. Gametes • formed by meiosis • haploid reproductive cells • humans: meiosis occurs in the testes and ovaries

35. Spermatogenesis: Male

36. Oogenesis: Female One Mature Egg Cell

37. Human Karotype

38. Asexual Reproduction • Production of offspring from one parent • Does not involve meiosis • Offspring are genetically identical to parent

39. Sexual Reproduction • Production of offspring through meiosis and the union of sperm and egg • Offspring are genetically different form parents • Genes are combined in new ways in meiosis • Evolutionary advantage is that it enables species to rapidly adapt to new conditions

41. Mitosis vs. Meiosis • Mitosis vs. Meiosis Animation

42. Nondisjunction • Failure of homologous chromosomes to separate properly during meiosis. • Both chromosomes of a homologous pair move to the same pole of the cell. • 1 gamete has an extra chromosome • Or • 1 gamete is missing a chromosome

43. Nondisjunction Animation • Nondisjunction Animation

44. 10-1 Mendel • Gregor Mendel • Austrian monk • Studied how traits are inherited from parents to offspring • Father of heredity • Chose garden peas for his meticulous experiments

45. Garden Peas • Reproduce sexually • W/ male & female gametes (sex cells) • Fertilization results in zygote • Becomes seed • Pollination male pollen transferred to female pistil

46. Monohybrid Cross • Hybrid- offspring of parents with different forms of a trait • Tall or short • crossed true-bred tall plants w/ true-bred short plants to get heterozygous offspring which then self-pollinated

47. Some Genes are Dominant • Some Genes Are Dominant click to play

48. Seven Traits of Peas

49. Mendel’s Rules • Alleles- different gene forms • Rule of Dominance • Dominant –observed trait • Recessive- disappearing or hidden trait

50. Mendel’s Rules • Law of Segregation • Every individual has 2 alleles of each gene w/ each gamete receiving 1. • During fertilization, gametes randomly pair to produce four combinations