Ncert Exercises & Solutions

Q.35 The harmful allele of sickle-cell anaemia has not been eliminated from human population. Such afflicted people derive some other benefit. Discuss.

Sickle-cell anaemia still persists in the population despite being harmful because this mutation can also be beneficial in certain conditions.

The mutant $H b^{5}$ type haemoglobin is found at high frequencies (up to 20% and above) in the tropical Africa.

It is known that heterozygotes ( ${H b}^{s} / {H b}^{A}$ ), having both types of haemoglobin show resistance to malarial infection because the body targets the Plasmodium falciparum infected cell for destruction. In contrast, individuals homozygous for normal haemoglobin
( $H b^{A} / {H b}^{A}$ ) suffer high mortality rates in early childhood due to malarial infection

Thus, the allele for sickle cells has been maintained because heterozygotes have a higher reproductive success than either of the two possible homozygotes.

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