Hardy-Weinberg Principle

Ø The frequency of occurrence of alleles of a gene in a population remains constant through generations unless disturbances such as mutations, non-random mating, etc. are introduced.

Ø Genetic equilibrium (gene pool remains constant) is a state which provides a baseline to measure genetic change.

Ø Sum total of all allelic frequencies is 1.

Ø Individual frequencies are represented as p and q such as in a diploid, where p and q represent the frequency of allele A and a.

Ø The frequency of AA is p², that of aa is q², and that of Aa is 2pq.

Ø Hence, p² + 2pq + q² = 1, which is the expansion of (p + q)².

Ø When the frequency measured is different from that expected, it is indicative of evolutionary change.

Ø Hardy-Weinberg equilibrium is affected by

o gene flow or gene migration

o genetic drift (changes occurring by chance)

o mutation

o genetic recombination

o natural selection

Ø Sometimes, the change in allele frequency is so prominent in the new sample of population that they become a different species and the original drifted population becomes the founder. This effect is called founder effect.

Ø The advantageous mutations that help in natural selection over the generations give rise to new phenotypes and result in speciation.