State and explain Hardy Weinberg's Principle.

Hint: Hardy Weinberg's Principle is also known as Hardy Weinberg equilibrium theorem or law in population genetics. For knowing if a population is in Hardy-Weinberg Equilibrium we have to observe at least up to two generations. If the allele frequencies are the same for both generations then the population is in Hardy-Weinberg Equilibrium undoubtedly.
So we have to think about the principles of this theorem.

Complete solution:
This principle states that allele frequencies in the population are stable and always constant from generation to generation. The gene pool that is total genes in the allele in the population remains a constant. This is called genetic equilibrium. The total sum of all the allelic frequencies is unit (1). Individual frequencies, for representation, can be named p, q, etc. In the case of diploid, p represents the frequency of allele A and q represents the frequency allele of a. The frequency of AA individuals in a population is simply ${p^2}$. This is simply stated in other ways, that is, the probability that an allele A with a frequency of p appears or both chromosomes of a diploid individual is simply the product of the probabilities, that is, ${p^2}$. Similarly aa is ${p^2}$, or Aa 2pq. Hence, ${p^2}$+2pq+${q^2}$=1. This is a binomial expansion of ${(p+q)^2}$. When the expected value differs from the measured frequency, the difference (direction) indicates the extent of evolutionary change. The disturbance is genetic equilibrium, or Hardy Weinberg equilibrium, that is, change of frequency of alleles in a population would then be interrupted as resulting in evolution.

Note:
Whenever migration of a section of the population to another place and population occurs, gene frequencies change in the original as well as in the new population in a random manner. New genes/ alleles are added to a new population and these are lost from the old population. If this gene migration happens multiple times then there would be a gene flow. If the scene change occurs by chance, it is called genetic drift.