Sickle - Sickle-Cell Case First example concerns classic...

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Sickle-Cell Case First example concerns classic case of sickle-cell anemia , a genetically transmitted blood disease common in some sub-Saharan African and So. Asian populations Sickle-cell gene involves change in molecular structure of hemoglobin, which alters shape of red blood cells, especially when oxygen supply drops (e.g., during strenuous exertion) Homozygotes (H s H s ) suffer from sickle-cell anemia and other complications, and thus have very low fitness (usually die before reproducing) Heterozygotes (H n H s ) have "sickle cell trait " -- a much less severe impairment, primarily evident under physiological stress of some kind Yet H s allele frequency is up to 30-40% in many W. African populations (mostly in heterozygotes) Such high gene frequencies could only be maintained by strong, consistent, and long- term selection in favor of heterozygotes, creating what population geneticists call a "balanced polymorphism" In turns out that the "balance" is due to fact that heterozygotes have lower rates of 1) malarial infection, and 2) malarial mortality if infected, compared to "normals" (H n H n ) In fact, studies have revealed that, because heterozygotes have higher reproductive
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This note was uploaded on 11/22/2011 for the course ANT ANT2000 taught by Professor Monicaoyola during the Fall '10 term at Broward College.

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Sickle - Sickle-Cell Case First example concerns classic...

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