notes 2-11-09

notes 2-11-09 - gUNIT 3 DISEASE*Genetic Disease A Classic...

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gUNIT 3- DISEASE **Genetic Disease: A. Classic examples all caused by alleles that are inherited caused by DND- usually inherited from both parents present in all body cells b/c inherited Usually everyone w/the disease genotype has the disease a. Ex. Cystic fibrosis: caused by a mutation in a gene for a protein that pumps chloride ions across a cell membrane out of lung cells and into lung mucus a.i. C= normal allele protein pumps a lot, water follows, mucus runny, helps lung to clear our pathogens (bacteria, viruses) a.ii. c= mutated allele thick, gummy mucus. ^risk lung infect’n, medial survival= 42-48 years old (usu. Have lung transplant) b. genotypes: CC- normal (homozygous dominant); Cc- normal carrier(heterozygous); cc- cystic fibrosis (homozygous recessive) b.i. 1/25 Euro. Am. are carriers b.ii. 1/1700 Af Am b.iii. 1/30,000 Asian Am b.iii.1. 1/625 Euro Am couples are both carriers (1/25 x 1/25) b.iii.2. 1/2500 babies should have cystic fibrosis (1/625 x ¼) c. Screening for genetic disease c.i. Ideally couples are screened for disease alleles prior to pregnancy (routine now for cys. Fib.) c.ii. If both parents are carriers options: c.ii.1. Not reproduce c.ii.2. Use sperm egg, donation c.ii.3. Selective abortion c.ii.4. In vitro fertilization followed by pre- implantation genetic testing c.iii. During pregnancy fetal cells can be sampled w/a needle (from amniotic fliud) fetus’ DNA studied B. Ex. Sickle cell anemia a. 1/12 Af. Am b. caused by mutation in hemoglobin gene protein in red blood cells carries O2 to cells CO2 away c. NOTATION D= allele for normal hemoglobin, round red blood cells; S= sickle allele mutated protein causes sickling of red blood cells (RBCs) at low O2 lvls c.i. DD & DS no sickle cell anemia SS sickle cell anemia c.i.1. S allele protects against malaria (RBCs invaded by malaria parasite sickle & are destroyed by body) => selcted for in Af ^freq in malaria prone parts Af (nat selec) C. Genetic disease can also be caused by a missing (monosome) or extra (trisomy) chromosome (not a whole set)
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a. Ex. Down Syndrome: trisomy 21 (all oter non-sex chromosome trisomies or monosomies are lethal) trisomy 21 less lethal b/c it is smaller b. 1/3000 women= XXX or X more or less normal. 1/1000 men= XXY or XYY Is it in your genes Distinguish between germ line and somatic mutations and explain role of somatic mutations in cancer. *germ line: variants in the DNA of egg, sperm,or both (present since conception) variant gene=^risk cancer *somatic mutation:changes in genes that develop during an indv lifetime. If certain group of cells accumulates it can become cancerous How do geneticists find genes (really, particular alleles of genes) that raise the risk of certain diseases. *twin studies, adoption studies and family studies *human genome project- we can hunt down and isolate genes and study them. Find out if genes are much more or less common in centenarians than in a group of ppl I their 70s (gene association studies) What is the biological reason that it is risky for cousins to marry and have kids?
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