HardyEssay -weinburg Equilibrium Essay - 1,085 words

The Hardy-Weinberg theorem states that the frequency of alleles and genotypes in a populations 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 original population. In the mouse example, a fire could have killed half of the population. Certain alleles would be overexpressed, certain underexpressed, and others not expressed at all. Which alleles are expressed occurs completely by chance.


Genetic drift in a new colony is called the founder effect. The population that results has a gene pool the expresses only those characteristics that the few founders carried with them, thus decreasing variability. If a few of the mice in the example were separated from their original population and colonized a new area, chances are that the founders of the new colony would not express the same genotype ratio in their gene pool as their original population. It is obvious that these types of genetic drift would become increasingly less meaningful as population size increases. For example, if 100 ...................................................................................................................................................................................................................................................................................................................................................................

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Essay Tags: equilibrium, natural selection, over time, gene flow, altering

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