(a ) Write the Hardy-Weinberg principle.
(b) Explain the three different ways in which natural selection can affect the frequency of a heritable trait in a population shown in the graph given below.

Explanation

( a) Hardy-Weinberg Principle : Hardy- Weinberg principle states that the gene pool (total genes and their alleles in a population) remain constant, i.e., the allele frequencies in a population are stable and constant from generation to generation. This biological phenomenon is called genetic equilibrium.
(b ) Natural selection can lead to stabilisation (in which more individuals acquire mean character value), directional change (more individuals acquire value other than the mean character value) or disruption (more individuals acquire peripheral character value at both ends of the distribution curve).