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Understanding Human Genetics & Meiosis

Explore human inheritance patterns, chromosomal disorders, and meiosis processes. Learn how DNA samples are obtained, and understand the correlation between chromosomes & genetic disorders. Discover the importance of crossing over and symbols in pedigrees.

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Understanding Human Genetics & Meiosis

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  1. Chapter 11 &14Human Geneticsand 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 B 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

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

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

  45. Symbols marriage Male Female

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

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

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

  49. Albinism – recessive disorder aa Aa Aa aa Aa Aa

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