1.  Human Genetics and Meiosis Oculocutaneous albinism The study of inheritance patterns in humans

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. 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.

16. Meiosis 1

17. Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II 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.

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

19. Prophase I: homologous chromosomes pairing into tetrads

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

21. 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.

22. Telophase I: membranes form around the separated homologues

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

24. Metaphase II: chromosomes align along the metaphase plate

25. Anaphase II: sister chromatids separate to opposite poles

26. 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 cel

27. Nondisjunction

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

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

30. 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.

31. More sibling similarities

32. What other chromosomal disorders can arise?  Deletion  Inversion  Translocation  Duplication

33. Chromosomal mutations Deletion Duplication Inversion Translocation

34. Problems with chromosomes  Duplication : copied parts of chromosome ABCDABCD ABBBCDABBBCD

35. Problems with chromosomes  Deletion : missing parts of chromosome ABCDABCD ADAD

36. Problems with chromosomes  Inversion : parts of chromosome tched ABCDABCD ACBDACBD

37. Human genetic disorders from deleterious genes  Sometimes the alleles inherited contribute to disorders and not from the number or shape of the chromosomes. 1. Sex-linked : genes found on X or Y chromosome 2. Recessive : requires 2 allele copies to express disorder 3. Dominant : requires only 1 allele copy to express disorder

38. Recessive disorders

39. Dominant disorder

40. Sex-linked disorder

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

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

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

45. Albinism – recessive disorder aaAa aaAa

46. Deafness – dominant disorder Aa or AA? Aa aa Mother must be AA.

47. Colored blindness – Sex linked XCXcXCXc XcYXcYXCXcXCXc XCYXCYXcXcXcXc XcYXcY

48. Let’s Review  http://www.cellsalive.com/mitosis.htm http://www.cellsalive.com/mitosis.htm  http://www.cellsalive.com/meiosis.htm http://www.cellsalive.com/meiosis.htm  http://www.biomanbio.com/GamesandLabs/Genegames/ snurfle_meiosis_and_genetics.html http://www.biomanbio.com/GamesandLabs/Genegames/ snurfle_meiosis_and_genetics.html