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Question

Sickle cell anemia has not been eliminated from the African population because


A
It provides immunity against malaria.
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B
It is controlled by dominant genes.
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C
It is controlled by recessive genes.
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D
Both A and C
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Solution

The correct option is C Both A and C
According to Hardy-Weinberg law, the composition of dominant and recessive genes would always remain the same. However, their frequency homozygosity may change. Moreover, the recessive genes would continue to play their role as their carriers and hence, continue in a population in certain parts of Africa today. The frequency of the mutant gene for sickle cell (HbS) is very high (5-20%). It is logical to think that natural selection would have eliminated the gene from the population. Sickle cell anemia is a genetic disease that slightly alters the structure of hemoglobin, the oxygen-carrying protein in red blood cells. This modified hemoglobin, when not carrying oxygen, tends to clump with other deoxygenated hemoglobin, deforming red blood cells and causing blood to clot throughout the body. The disease is prevalent in Africa where incidence of malaria is high because sickle cell anemia imparts some resistance to malaria. Thus the correct answer is option D.


Biology

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