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 13, 15, 18, 21, 22

trisomy 21 and 22 may be survivable into adulthood

3. nondisjunction of sex chromosomes:

Klinefelter syndrome: XXY

Turner syndrome: XO

YY gametes (sperm)  XYY

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

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

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

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

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

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

Cystic fibrosis PKU

Inbreeding increases the likelihood of recessive disorders.

Dominant disorders: Huntington’s disease Achondroplasia

Pedigrees:

Amniocentesis: performed between weeks 14 and 20.

CVS: performed as early as 8 weeks.

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