Suppose that, with regard to a particular gene with two alleles, a and a, we know that 60% of the alleles in the gene pool of a particular large population are a. we observe this population for five generations, during which we know that no mutation, selection, or migration has occurred. after this period, the frequency of the a allele is expected to be

0.4
0.25
0.16
0.6

The correct answer is: 0.4

This is an example of Hardy-Weinberg Principle in which genotype and allele frequencies in populations are not evolving. This means that frequencies remain constant from generation to generation in the absence of evolutionary influences such as genetic drift, mate choice, natural selection, sexual selection, mutation, gene flow, meiotic drive, population bottleneck, founder effect…

According to this principle, there is also HW equilibrium:

P2+2pq+q2=1 or p+q=1 where p is the frequency of one allele, q is frequency of another allele; p2 is the frequency of one homozygous genotype (q2 of another) and 2pq is frequency of heterozygous genotype.