Into maybe a different, a new type of trait, Generation turning into another one, or turning One of these alleles can't, isn't from generation to We're also going to assume no mutation, so we're going to assume that One of the alleles or another are going to be more or less likely to reproduce and have viable offspring. That there's no selection, no natural selection is, orĮven unnatural selection, is going on that would change That, we're gonna make some assumptions, and theseĪre all just assumptions that get us a stable alleleįrequency in the population from generation to generation. And it really builds on the work we've already seen withĪllele frequencies. Or homozygous dominant, or might be a heterozygote. Principle, which is a really useful principle for thinking through what allele frequencies mightīe, or what probability you would have if you found someone, what percentage of the population might be homozygous recessive, of the HOMOZYGOUS RECESSIVE GENOTYPEįamiliar with the idea of allele frequency, let's build on that to develop the Hardy,ĭo this in a new color, and actually, let meĭo it right over here, the Hardy Weinberg The total of all genotypes should be equal to 1 so In gene pool that include allele p and q the possible genotypes are p+q=1 since the sum of both frequencies is 100%. In order to express Hardy Weinberg principle mathematically, suppose "p" represents the frequency of the dominant allele in gene pool and "q" represents the frequency of recessive allele. Hardy and William Weinberg, who suggested some assumptions for stable, non evolving population in which "allele frequencies do not change and therefore evolution does not occur". In reality Homozygous PC deficiency is exceptionally rare although more frequent in countries where consanguineous marriage is common.It is a conceptual idea of population equilibrium that was developed by 2 scientists G.H. So in this example 1/25 of the population are heterozygous for the PC allele and would have potentially low PC levels. The frequency of heterozygotes is derived from 2pq = 2 x 0.02 x 0.98 = 0.04. The frequency of p must be 1-0.02 which is 0.98 and so this is the frequency of the normal allele in the general population.ģ. This is the frequency of the recessive allele in the general populationĢ. If we remember that p 2 + q 2 + 2pq = 1 and in this case p is the frequency of the allele and q the frequency of the allele, then:ġ. We will designate the normal allele p as and the mutant allele q as From this we can calculate the frequency of heterozygous and homozygous individuals. This is a rare disorder but for this example let us assume that it affects 1/2500 births in the UK. Of their offspring 25% will be homozygous, 25% will be homozygous and 50% will be heterozygous as shown in the probability table below:Ĭonsider the case of homozygous Protein C deficiency. If we consider two individuals that are heterozygous for a specific trait which we will designate then during meiosis and the creation of gametes, 50% will contain the allele and 50% the allele. No selection can occur so that certain alleles are preferentially selected or not selected The population must be sufficiently large so that no genetic drift (random chance) can cause the allele frequencies to change.ĥ. No mutations must occur so that new alleles do not enter the population.Ĥ. In order for the equilibrium to continue the following conditions require to be met:ġ. The Hardy-Weinberg principle states that in any population allele and genotype frequencies remain constant i.e.
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