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Hardy-Weinburg Equilibrium

Uploaded by saritagarcia113 on Feb 10, 2001

The Hardy-Weinberg theorem states that the frequency of alleles and genotypes in a population’s gene pool remain constant over the generations unless acted upon by agents other than sexual recombination. For example, take a population of mice that consists of 1,000 members. A specific allele, albino allele, is recessive within this species. 80% of the population expresses the normal phenotype- brown coloring, while the remaining 20% are albino. 640 members of the population have the genotype AA, 320 have Aa, and 40 have aa. If completely random mating were to occur, there would be an 80% chance that a gamete would bear the normal allele, A, and a 20% chance that the gamete would bear the albino allele, a. The resulting offspring will display the following genotype ratios: AA will have 64%, Aa 32% (the chance of the offspring having the A allele is 96%), and aa 4%. The offspring have the same genotype ratio as their parents. This example was one of Hardy-Weinberg equilibrium. The next generation will express the same genotype ratio as their parents, and so on. But what exactly is needed to create Hardy-Weinberg equilibrium? (Basically, a population in Hardy-Weinberg equilibrium s not evolving in any way.) Five specific factors are needed to create Hardy-Weinberg equilibrium within a population- a very large population, isolation from other populations, no net mutations, random mating, and no natural selection.

The first element needed to create Hardy-Weinberg equilibrium is a very large population size. The larger the population, the less likely it is for genetic drift to occur. Genetic drift is a chance fluctuation in the gene pool that may change the frequencies of alleles. A large population can better represent the gene pool of the previous generation than a small one. In order to completely eliminate all chances of genetic drift, a population would have to be infinitely large. Thus, we can see here that perfect Hardy-Weinberg equilibrium, which has no changes in the frequency of alleles, would require no genetic drift at all, and genetic drift itself is only possible in a population of infinite size. There are two types of genetic drift- the bottleneck effect and the founder effect. Both severely decrease the variability within a population, altering the frequencies of alleles and thus making Hardy-Weinberg equilibrium impossible. If a disaster occurs in a population, killing off many members, the surviving members will not be representative of the...

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Uploaded by:   saritagarcia113

Date:   02/10/2001

Category:   Biology

Length:   5 pages (1,099 words)

Views:   2287

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