![]() ![]() ![]() This occurs because q 2 is much smaller than 2 pq when q is close to zero. Another implication of the Hardy–Weinberg principle is that rare alleles are more likely to be found in heterozygous individuals than in homozygous individuals. Third, it is important to note that dominant alleles are not always the most common alleles in a population. A second implication is that the Hardy–Weinberg principle allows one to determine the proportion of individuals that are carriers for a recessive allele. Most importantly, genetic variation is conserved in large, randomly mating populations. There are a number of evolutionary implications of the Hardy–Weinberg principle. After a single generation of random mating Hardy–Weinberg proportions are obtained. A alleles are shown as black half-circles and B alleles are shown as gold half-circles. AA homozygotes (black circles), AB heterozygotes (black and gold circles), and BB homozygotes (gold circles) contribute to the gene pool. Note that there are two ways that an individual can be an AB heterozygote: they can either inherit an A allele from their mother and a B allele from their father or they can inherit a B allele from their mother and an A allele from their father.įigure 2. Mathematically this involves the binomial expansion: ( p + q) 2 = p 2 + 2 pq + q 2 (see the modified Punnett Square in Figure 1 for a graphical representation). Because the allele that an individual receives from their mother is independent of the allele they receive from their father, the probability of observing a particular genotype is found by multiplying maternal and paternal allele frequencies. ![]() In a randomly mating population without natural selection, offspring genotypes are found by randomly sampling two alleles from this gene pool (one from their mother and one from their father). Here, individuals contribute alleles to an infinitely large pool of gametes. One useful way to think about the Hardy–Weinberg principle is to use the metaphor of a gene pool ( Crow, 2001). When these assumptions are violated, departures from Hardy–Weinberg proportions can result. The Hardy–Weinberg principle relies on a number of assumptions: (1) random mating (i.e, population structure is absent and matings occur in proportion to genotype frequencies), (2) the absence of natural selection, (3) a very large population size (i.e., genetic drift is negligible), (4) no gene flow or migration, (5) no mutation, and (6) the locus is autosomal. In the absence of other evolutionary forces (such as natural selection), genotype frequencies are expected to remain constant and the population is said to be at Hardy–Weinberg equilibrium. The Hardy–Weinberg principle states that after one generation of random mating genotype frequencies will be p 2, 2 pq, and q 2. The frequency of allele A is denoted by p and the frequency of allele B is denoted by q. Imagine that you have a population with two alleles ( A and B) that segregate at a single locus. The Hardy –Weinberg principle relates allele frequencies to genotype frequencies in a randomly mating population. Lachance, in Encyclopedia of Evolutionary Biology, 2016 The Hardy–Weinberg Principle ![]()
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