Natural selection affects Hardy Weinberg Equilibrium principle which states that in sexually reproducing organisms the allele frequency is stable and is constant from generation to generation under certain conditions of stability. The gene pool, Le.. total genes and their alleles in a population remains constant. This is called genetic equilibrium. Natural selection is a process in which heritable variations enabling better survival are enabled to reproduce and leave greater number of progeny. Natural selection can lead to
(i) Stabilisation in which more individuals acquire mean character value.
(ii) Directional change in which more individuals acquire value other than the mean character value, le., towards one of the two extremes of the distribution curve.
(iii) Disruption in which more individuals acquire peripheral character value at both ends or extreme ends of the distribution curve.
The other four factors that disturb the genetic equilibrium are:
(i) Gene migration/flow. When migration of a section of population to another place occurs, there is change in gene frequencies.
(ii) Genetic drift. The random changes in gene frequency in a population occurring by chance alone rather than by natural selection. ltbr. (iii) Mutation. Pre-existing advantageous mutations when selected will result in observation of new phenotypes and over few generations this would result in speciation.
(iv) Recombination. Variations due to recombination during gametogenesis result in change frequency of genes and alleles in future generations.
