Question

Use a numerical example to demonstrate that selection is not efficient at removing deleterious recessive alleles from a population.

First, choose a value of q, the frequency of the deleterious recessive allele in generation 1. What fraction of the population is homozygous for the deleterious recessive?

Now, select a value for s and calculate the expected frequency of the allele in the next generation, q’. What fraction of the population is homozygous for the deleterious recessive in this generation?

Answer 1

Selection can't completely wipe out a lethal recessive allele. This is because the alle will remain in th epopulation which is heterozygous to the allele. Only homozygous individuals ill suffer and die. Heterozygous individuals will ot suffer from the disease and hence survive, This results in the allele remaining in the population. Example of such a an allele still present in the population is sickele anaemia. A person homozygous to the sickele cell RBCs will suffer from the disease and die. But heterozygous individuals are normal and hence the allele remains in the population and gets inherited. The disease is very common in African countries and India. Carriers of the disease contribute to 10-30% of the people in these regions. If the natural selection can remove the deleterious alleles, the sickle cell allele should have been completely wiped out. But, the carriers are perfectly normal. That is why the all carriers or heterozygous individuals survive and retain the allele in the population. Even now there are about 2% of births happen with babies having sickle cell disease.