Assigned Readings Unfortunate Drift Ashkenazi Jews Central and Eastern Europe origin. Many American Jews Unique set of genetic diseases. Best known is Tay-Sachs At least 9 others. Most are caused by recessive genes. Symptoms only appear if 2 copies of the recessive gene are present. One copy does no harm, may even do good. One copy of Tay-Sachs protects from Tuberculosis. Neil Risch proposes that mutant genes may have become concentrated in Ashkenazi?s by chance or historical accident. Genetic Drift Idiopathic Torsin Dystonia (ITD) Causes involuntary muscle contractions. Dominant A single copy is enough to create symptoms. Usually doesn?t though?reasons unknown. Only 30% show symptoms. Survives in the populations but doesn?t convey an advantage. German Jews moved to Eastern Europe and were a generally small population. Didn?t marry outside the population. Founder Effect: a small group passes on their mutations and makes them more concentrated in the larger group. 90% of the families had the same genetic marker. ITD came from 1 single mutation. Inherited from the same mutation. Mutation occurred recently. After the migration to Eastern Europe. Not all Jews left equal numbers of children. The original ITD mutation occurred in an affluent family in which produced more descendants. Poor families produced less descendants. Created the concentration change of the gene from 1/100,000 to 1/3,000 He also proposes genetic drift and natural selection mutually account for the concentration of recessive diseases. French Canadians have the same genetic drift with Tay-Sachs.
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