Question

Natural selection tends to reduce genetic variation within a population by disfavouring particular alleles. However, in some situations selection can help maintain genetic variation rather than erode it. Explain how this can happen using an example.

Answer 1

Some forms of natural selection maintain genetic variation rather than eliminating it. Frequency-dependent selection is one of them. Large number of alleles are generated at a single locus. Multiallelic polymorphism is generated with wide range of allele-frequency distribution, therefore genotypic fitness. Negative frequency-dependent selection helps favoring rare genotypes and promoting genetic variation of the population.

Trypanosoma brucei​, an African sleeping sickness parasite changes its surface antigens as the host develops antibodies. Most common antigens are targeted by the host antibodies. Frequency-dependent selection maintains genetic diversity of the parasite's antigens and its host's antibodies.