How do you use the Hardy-Weinberg principle?

Question

Piper Anderson · Accepted Answer

Hardy Weinberg principle is used to derive frequencies of different alleles of a particular gene, within a subpopulation and it also helps to determine genetic load.

The Hardy Weinberg principle, also referred to as HW equilibrium by population geneticists, is the theory that, in the absence of active evolutionary forces, the frequencies of distinct alleles of a gene will remain constant in a population generation after generation. The frequency of allele B is represented by p, and that of allele b is represented by q, if we consider a gene with two alleles: b is a recessive allele and p is a dominant allele. Obviously, p plus q would always add up to 1. In line with HW law: #(p+q)^2#= #p^2 + 2pq + q^2 # = 1 #p^2# is the frequency of homozygous dominant individuals BB #2pq# is the frequency of heterozygous dominant individuals Bb #q^2# is the frequency of homozygous recessive individuals bb The idea inlaid in HW law is used in demographic studies, to determine allele frequencies. In a subpopulation(=deme), recessive individuals (bb) are easily identified due to phenotypic difference from dominant individuals (BB, Bb), hence #q^2# is known. Thus frequency of recessive allele ( q ) could be determined. As we know that p+q=1, and as q is known, frequency of dominant allele ( p) could also be determined. Let us consider the example of albinos in a small population where there is one albino in every hundred individuals (#q^2# = 1/100 = 0.01), which means frequency of recessive allele is 0.1 (#q# = 0.1). That means frequency of dominant allele for normal skin color is 0.9 (as p+q = 1). [Please note this is a hypothetical proposition, could be possible in isolated population: in the world 1 in 20,000 are albino]. Now, even though you only see one person with the condition, you can see that there are 2pq, or 2x0.9x0.1, or 18/100, heterozygous dominant individuals in this population who are all carriers of the allele that causes albinism. As a result, HW law also aids in determining "genetic load," or the likelihood that an unwanted allele will exist in the gene pool.

Lydia Adams · Answer

undefined Calculate allele frequencies and predict genotype frequencies in a population under conditions of no evolution, assuming factors like mutation, migration, selection, and genetic drift are absent. Use the Hardy-Weinberg equation: $ p^2 + 2pq + q^2 = 1 $, where $ p $ and $ q $ represent the frequencies of the two alleles in a gene pool.