Question

In a Hardy-Weinberg population, the frequency of allele A of gene Aa is 0.4. What is the frequency of allele a?
A. 0.6
B. 0.48
C. 0.16
D. 0.36

Answer 1

Hint: The Hardy-Weinberg equilibrium states that the genetic variation in a population will remain constant from one generation to the next generation if there are no disturbing factors. When, in a large population, mating is random and there are no disruptive circumstances, the law predicts that both the genotype and the allele frequencies will remain constant. This would happen because they are in a state of equilibrium.

Complete answer: Frequencies of alleles are calculated using the Hardy-Weinberg relation. It states that the sum of allelic frequencies is equal to one.
So,
$\begin{gathered}
\Rightarrow p + q = 1 \\
\Rightarrow p = 1 - q \\
\end{gathered} $
Let the allelic frequency of A in the gene Aa be “p”. Therefore, the allelic frequency of “a” in the gene “Aa” can be assumed to be “q”.
So, according to the above relation, we can calculate the allelic frequency of a to be:
$\begin{gathered}
\Rightarrow p = 0.4 \\
\Rightarrow q = 1 - 0.4 \\
\Rightarrow q = 0.6 \\
\end{gathered} $
Hence, the correct answer is option A.

Additional information: The Hardy-Weinberg equilibrium can be disturbed by a number of forces. They are;
a. Mutations
b. Natural selection
c. Non-random mating
d. Genetic drift
e. Gene flow

Note: Hardy-Weinberg equilibrium is a concept that is hardly applied in any real situations because it is nearly impossible to find a population where any of the above factors are not present. So, this principle remains largely a theoretical concept and not a practically seen phenomenon.