In a population of $5000,200$ individuals exhibit a trait for recessive allele 'a'. Find out the frequency of the dominant and recessive alleles in the population.

The correct option is C $0.8$ and $0.2$
According to the Hardy-Weinberg law, the allele and genotype frequencies in a population remain constant under the absence of factors responsible for evolution. It states that the sum of all genotype frequencies can be represented as the binomial expansion of the square of the sum of p and q. This sum is equal to one.
(p + q)2 = $p^2$ + 2pq + $q^2$ = 1.
Here, "p" is the frequency of the dominant allele, $p^2$ is the frequency of homozygous dominants, q is the frequency of recessive allele and $q^2$ is frequency of homozygous recessive individuals. The "2pq" in equation shows frequency of heterozygotes in the population. In the question, the genotype frequency of recessive population is ($q^2$) = (200/5000*100= 4% or 0.04). Hence, frequency of recessive allele= q= √0.04= 0.2. Since p+q=1; thus the frequency of dominant allele = p = 1 - q = 1 - 0.2 = 0.80.
The correct option is A.