1. Chapter 11 &14 Human Genetics and Meiosis
The study of inheritance patterns in humans
Oculocutaneous albinism

2. What each of the human chromosomes look like

3. Karyotype: A photomicrograph of chromosomes arranged according to a standard classification

4. In other words…
Chromosomes are digitally arranged so that they are matched with their homologue or “partner” chromosome.
Homologue chromosomes are the same size, shape, and carry the same genes, and one is inherited from each parent.
They are numbered according to size.

5. Sex determination with karyotype
This karyotype has 23 exact pairs, which means the person is female.
Note that #23 chromosomes are both X.

6. Normal human male
Note that #23 chromosomes are X and Y.

7. Is this person female or male?

8. Trisomy 21 Abnormality shown in karyotype
Note that there are three copies of #21 chromosome.
This person has Down Syndrome.

9. Photos of Down Syndrome patients from the National Down Syndrome Society

10. Correlation between mother’s age and Trisomy 21 incidence

11. Monosomy X Abnormality shown in karyotype
Note this person only has 1 copy of the X chromosome.
This female has Turner’s syndrome.

12. XXY Male (Extra X)

13. How are DNA samples obtained for karyotypes?

14. Amniocentesis: obtaining amniotic fluid which has cells from the fetus

15. Chorionic villi sampling: removing cells from the chorion with fetal tissue

16. If there are chromosomal number abnormalities, how do they form?
Meiosis: the process of creating sperm or egg from a diploid cell
If there is a mistake when chromosomes are separating, then the resulting sperm or egg will have too many or too few chromosomes.

17. Click on image to play video.

18. Meiosis 1

19. Meiosis II Prophase II Metaphase II Anaphase II Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

20. Oocyte or Spermatocyte
This cell that can undergo meiosis originally has 6 chromosomes and has replicated to 12 chromosomes in preparation for meiosis.

21. Prophase I: homologous chromosomes pairing into tetrads

22. Metaphase I: tetrads align, along the metaphase plate

23. Anaphase I: homologous chromosomes separate from the metaphase plate
If chromosomes do not properly separate, this is called nondisjunction.
Nondisjunction leads to trisomy and monosomy disorders.

24. Telophase I: membranes form around the separated homologues

25. Prophase II: spindle fibers bind to the sister chromatids of each chromosome

26. Metaphase II: chromosomes align along the metaphase plate

27. Anaphase II: sister chromatids separate to opposite poles

28. Telophase II: nuclear membrane forms around newly separated chromatids
Note that each new nucleus formed has ½ the amount of DNA as the original cell.
These cells are haploid cells.

29. Nondisjunction

30. How can siblings look alike but not exactly the same if they come from the same parents?

31. Crossing over
The chromosomes during prophase I undergo crossing over, where parts of the homologues randomly switch places.

32. Importance of crossing over
The gene combinations that a person gets from his or her parents will be different, to varying degrees, than the combination a sibling may get.

33. More sibling similarities

34. What other chromosomal disorders can arise?
Deletion
Inversion
Translocation*
Duplication
*Don’t worry about this one.

35. Chromosomal mutations
Deletion
Duplication
Inversion
Translocation

36. Problems with chromosomes
Duplication: copied parts of chromosome A B C D A B C D

37. Problems with chromosomes
Deletion: missing parts of chromosome A B C D A D

38. Problems with chromosomes
Inversion: parts of chromosome tched A B C D A C B D

39. Human genetic disorders from deleterious genes
Sometimes the alleles inherited contribute to disorders and not from the number or shape of the chromosomes.
Sex-linked: genes found on X or Y chromosome
Recessive: requires 2 allele copies to express disorder
Dominant: requires only 1 allele copy to express disorder

40. Recessive disorders

41. Dominant disorder

42. Sex-linked disorder

44. Are you red-green color blind?
Yes, if you have a difficult time distinguishing a number from this picture

45. Pedigrees: a chart which can show trait inheritance through several generations
Albinism

46. Symbols
marriage
Male
Female

47. More symbols
She gave birth!
Pain! Suffering!

48. Even more symbols
… and they have a litter of 4!

49. Still more symbols
Affected. AA or aa
Normal heterozygous

50. Albinism – recessive disorderaa Aa Aa aa Aa Aa

51. Deafness – dominant disorderaa
Aa or AA?
Mother must be AA. Aa Aa Aa Aa

52. Colored blindness – Sex linked
XcY
XCXc
XcY
XCXc
XCY
XcXc

53. Pedigree of Hsu family
Me!

54. Review Videos

55. Click on image to play video.

56. Click on image to play video.

57. Click on image to play video.

58. Click on image to play video.