a. Hardy–Weinberg principle states that the gene pool (total genes and their alleles in a population) remains 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).
Diagrammatic representation of the operation of natural selection on different traits: (a) Stabilising (b) Directional and (c) Disruptive