Question

The frequency of a recessive allele in a large randomnly mating population is 0.2. What is the frequency of (a)The dominant allele?(b)The hetrozygote?

Answer 1

Hardy Weinberg Law and HW equation is helpful to calculate various things :-
As per Hardy Weinberg equation the Sum of the allele frequency for all the alleles at the locus must be 1.

**If frequency of dominant allele A is p and frequency of recessive allele a is q then as per HW equation
In Large random mating population:-

p+q=1
As per your question the frequency of recessive allele a ie q is 0.2
Then :- As
p+q=1
P=1-q
P=1-0.2
P=0.8 is the answer as the frequency of dominant allele.

The frequency of all three types of Genotypes can be found:----
As per the Hardy Weinberg equation
p2+2pq+q2=1
Where p2 is the frequency of Homozygous dominant Genotypes
2pq is the frequency of Heterozygous Genotypes
And
q2 is the frequency of Homozygous recessive Genotypes
But you ask 2nd question about
Frequency of Heterozygous Genotypes ie 2pq can be found
2pq =2×0.8×0.2
=2×0.16
=0.32 is the frequency of Heterozygous Genotypes

Likewise p2 and q2 frequency of Homozygous dominant and frequency of Homozygous recessive Genotypes can also be found.

Hope it helps.
Thanks