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2-11-09 - a geographical association between the...

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2/12/09 D. Evolution of relationship between sickle cell allele and malaria 1. Slash-and-burn agriculture created conditions for proliferation of  mosquitos, which led to natural selective advantage of sickle cell allele in  heterozygotes. E. Other red blood cell anomalies and malaria 1. Thalassemia and deficiency/absence in G-6-PD a. Thalassemia is abnormality in the production of hemoglobin.  Homozygosity for thalassemia results in early death. Heterozygotes  show a range of responses from phenotypic normality to severe  anemia.  b. G-6-PD is an enzyme in red blood cells. Individuals are  phenotypically normal with absence/deficiency in G-6-PD. 2. Selective advantage of thalassemia and G-6-PD deficiency with respect to  malaria is based on:
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Unformatted text preview: a. geographical association between the distribution of polymorphic levels of these red blood cell anomalies and malaria b. clinical and experimental evidence suggesting that these red blood cell anomalies provide a lethal environment for the malarial parasite c. Balanced polymorphism for thalassemia explains the perpetuation of this red blood cell variant F. Conclusions 1. Natural selection is opportunistic. That is, selection acts only on the existing phenotypic/genotypic variation in a population. Therefore, there can be different roots of adaptation to the same environmental stress. (ex: malaria and three red blood cell variants- sickle cell, thalassemia, and G-6-PD deficiency. END OF TEST 1!!!...
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