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

3. 1. nondisjunction leads to aneuploidy

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

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

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

7. trisomy 21 and 22 may be survivable into adulthood

9. 3. nondisjunction of sex chromosomes:

10. Klinefelter syndrome: XXY

11. Turner syndrome: XO

12. YY gametes (sperm)  XYY

13. XX gametes  XXX

14. OY  not viable

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

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

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

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

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

21. 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

22. Cystic fibrosis PKU

23. Inbreeding increases the likelihood of recessive disorders.

24. Dominant disorders: Huntington’s disease Achondroplasia

25. Pedigrees:

26. Amniocentesis: performed between weeks 14 and 20.

27. CVS: performed as early as 8 weeks.

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