Question

Q5. Which of the following is FALSE?

If a genetic disease reduces fertility and the allele that causes the disease offers no other advantage, the allele will likely eventually disappear, due to natural selection.

Natural selection does not favor individuals who are homozygous for the sickle-cell allele, because these individuals typically die before they are old enough to reproduce.

Individuals who are heterozygous HbA/HbS are protected from malaria, and this is why sickle-cell anemia persists in wetter, mosquito-prone regions in Africa.

In regions where malaria does not occur, individuals who are heterozygous HbA/HbS have a selective advantage over those who are homozygous for the normal hemoglobin allele (HbA).

Answer 1

1) True

If the disease reduces fertility, the chances of affected individual passing it on to children is decreased. This therefore, offers no advantage and would be eventually disappear.

2) True

Individuals who are homozygous for the sickle-cell allele have a range of health problems that often cause early mortality, cancelling out the beneficial features of this allele.

3) True

Individuals who are heterozygous HbA/HbS are protected from malaria, and this is why sickle-cell anemia persists in wetter, mosquito-prone regions in Africa. This gives them the fitness feature which becomes more prevalent with passing years.

4) False

The advantage is solely based upon the selection pressure of malaria. Without this selection there is no advantage of having a copy of the sickle cell allele over the normal allele.

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