Question

The dynamics are different when the advantageous allele is rare, compared to when it is near 100%. Explain what happens when a recessive advantageous allele is rare versus near fixation

Answer 1

An advantageous allele might be dominant or recessive in population. In case of dominant advantageous allele the dynamics is relatively simple because being dominant the allele is expressed both in homozygous and heterozygous condition. Combined with the advantage of natural selection, its frequency increases rapidly.

However, recessive advantageous allele does not increase rapidly because despite being advantageous it gets masked by the dominant allele. When it is rare, it is present in very less number of recessive homozygotes and in slightly more number as heterozygotes. Over the generations, natural selection selects the recessive allele so the number of heterozygotes start to increase slowly. Recessive homozygotes are still rare because they need both the copies of recessive allele. Eventually recessive homozygotes also start increasing in number which leads to the fixation of recessive allele in the population.