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

14. B. Hemophilia
- loss of any of 12 clotting proteins
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

19. 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

20. Cystic fibrosis
PKU

21. Inbreeding increases the likelihood of recessive disorders.

22. Dominant disorders:
Huntington’s disease
Achondroplasia

23. Pedigrees:

24. Amniocentesis: performed between weeks 14 and 20.

25. CVS: performed as early as 8 weeks.

26. 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