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Nondisjunction

Nondisjunction. A. Failure to separate homologous chromosomes during Meiosis. 1. nondisjunction leads to aneuploidy. 2. nondisjunction of autosomal chromosomes:. a. monosomics. 2. nondisjunction of autosomal chromosomes:. b. trisomics. if one of the 5 smaller ones, somewhat viable.

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Nondisjunction

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  1. Nondisjunction A. Failure to separate homologous chromosomes during Meiosis

  2. 1. nondisjunction leads to aneuploidy

  3. 2. nondisjunction of autosomal chromosomes: a. monosomics

  4. 2. nondisjunction of autosomal chromosomes: b. trisomics

  5. if one of the 5 smaller ones, somewhat viable 13, 15, 18, 21, 22

  6. trisomy 21 and 22 may be survivable into adulthood

  7. 3. nondisjunction of sex chromosomes:

  8. Klinefelter syndrome: XXY

  9. Turner syndrome: XO

  10. YY gametes (sperm)  XYY

  11. XX gametes  XXX

  12. OY  not viable

  13. Mutations A. Random changes in genes 1. rare 2. usually recessive

  14. B. Hemophilia - loss of any of 12 clotting proteins (genes) 1. recessive 2. 2 important clotting genes are sex-linked

  15. C. Sickle-cell disease (anemia) 1. caused by defective hemoglobin mutation of one allele causes a single amino acid change

  16. C. Sickle-cell disease (anemia) 2. those homozygous for the sickle-cell allele will have the disease

  17. C. Sickle-cell disease (anemia) 3. those heterozygous are basically normal pleiotropy: when a gene produces multiple effects advantage in resisting malaria

  18. D. Tay-Sachs 1. caused by a recessive allele 2. leads to deterioration of the nervous system (8 months) 3. increased incidence in certain populations certain Jewish populations in U.S. : 1 in 27 people of Jewish descent carriers 1 in 250 in general population

  19. Cystic fibrosis PKU

  20. Inbreeding increases the likelihood of recessive disorders.

  21. Dominant disorders: Huntington’s disease Achondroplasia

  22. Pedigrees:

  23. Amniocentesis: performed between weeks 14 and 20.

  24. CVS: performed as early as 8 weeks.

  25. Blood tests: 1. alpha-fetoprotein (AFP) high in neural tube defect low in Down syndrome 2. triple screen (now quad screen) - can even indicate trisomy 18 risk 3. these tests are not diagnostic, only reflective of risk

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