Write short note on Hardy - Weinberg principle.
 

In $1908$, $GH$ Hardy and $W$. Weinberg established a simple mathematical relationship to the study these genes frequencies and gave Hardy - Weinberg principle.

This principle states that the allele frequencies in a preparation are stable and is constant for generation to generation i.e. gene pool remains constant.

This is called genetic equilibrium or Hardy - Weinberg equilibrium.

In a given population one can find out the frequency of occurance of allele of a gene or locus.

This frequencies is supposed to remain fixed and even remain the same through generations.

Hardy - Weinberg principle stated it using algebraic equations.

This principle says that allele frequencies in a population are stable and is constant from generation to generation.

The gene pool (total genes and their allele in a population) remains a constant.

This is called genetic equilibrium.

Sum total of all allelic frequencies is $1$ .

Individual frequencies, for example can be named $\mathrm{p}, \mathrm{q}$ etc.

In a diploid, $p$ and $q$ represent the frequency of allele $A$ and allele $a$.

The frequency of $AA$ individuals in a population is simply $\mathrm{P}^{2}$.

This is simply stated in another ways i.e. the probability that an allele A with a frequency of P appear on both the chromosomes of a diploid individual is simply that product of the probabilities i.e. $\mathrm{P}^{2}$.

Similarly of $\mathrm{a}^{\mathrm{a}}$ is $\mathrm{q}^{2}$, of Aa. $2 \mathrm{pq}$

Hence $\mathrm{P}^{2}+2 \mathrm{Pq}+\mathrm{q}^{2}=1$

This is a binomial expansion of $(\mathrm{p}+\mathrm{q})^{2}$

When frequency measured, differs from expected values the difference (direction) indicates the extent of evolutionary change.

Disturbance in genetic equilibrium or Hardy - Weinberg equilibrium i.e. change of frequency of alleles in a population would then be interpreted as resulting in evolution.

Factors affecting Hardy - Weinberg equilibrium : Five factors are known to affect Hardy - Weinberg equilibrium.

These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection.