Question

As in humans, deleterious alleles can persist in a population. What are processes that account for this, in addition to, deleterious recessive alleles hiding in heterozygous carriers?

Answer 1

There are some processes by which deleterious alleles remain in human population. These are discussed below:

a. In some cases the deleterious genes found tho be linked or lie in between two beneficial gens and thus it is not possible to eliminate such genes from the population by natural selection.

b. In some population , deleterious allele for one disease give advantage for another disease. For example, sickle cell allele, in some countries of Africa, give survival advantage to the persons who carry the allele in heterozygous condition. This is called heterosis or heterozygous advantage.

c. Some deleterious alleles may be fixed when genetic drift occurs. In genetic drift, small portion of the gene pool get isolated from whole population. In such cases alleles are fixed without selective value for that allele. So, if any such deleterious allele become separated by genetic drift, the frequency of such alleles may increase over time and it will be remain in population.

d. Deleterious alleles may remain in carrier individuals. In many persons, these alleles remain under the dominant allele where it is not expressed as it is recessive in nature. It will only express in homozygous recessive condition. Therefore this allele is not lost from the population due to its hidding nature in heterozygous condition.