question_answer 52)

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

Answer:

                  Sickle-cell anaemia still persists in the population despite being harmful because this mutation can also be beneficial in certain conditions. The mutant  type haemoglobin is found at high frequencies (up to 20% and above) in the tropical Africa. It is known that heterozygotes (), having both types of haemoglobin show resistance to malarial infection because the body targets the Piasmodium falciparum infected cell for destruction. In contrast, individuals homozygous for normal haemoglobin () 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.