Hardy Weinberg Lab Report

Investigation of Hardy-Weinberg theorem and evolutionary mechanisms

Madison Gladden

03/04/2016

Genetics

Dr. Yamashita

Introduction: The change in allele frequency in populations over time is an observable sign of evolution. These changes in allele frequency can be measured in a population. The Hardy-Weinberg model (p2 + 2pq + q2 = 1) proposes that the frequencies should stay the same if the conditions are met. These conditions include no mutations, no immigration or emigration, random mating, no natural selection, and a large sample size. In reality, populations will not adhere to the Hardy-Weinberg conditions in most aspects. Many conditions and events can alter the allelic frequency of a population

Eventually, the recessive allele, q, becomes fixed in the population. The gene flow experiment showed that the allele frequencies change for every generation, when gene flow migration takes place into and out of the population. The allele frequencies alternated between the two populations. The founder effect shows that one allele (p) became more prevalent in the populations than the other (q). The industrial melanism shows that the allele p became steadily more prevalent in the population over the generations. The sickle-cell anemia shows that one allele (p) increased in frequency almost linearly, while the other (q) decreased in a similar fashion. A simulation of gene flow between five populations shows that allele p becomes fixed in populations 1, 3, 4, and 5. The p allele is lost in population

In the bottleneck experiment, a “natural disaster” causes a drastic decrease in the population. The surviving allele frequencies establish the next generation. The p allele is eventually lost and the q allele becomes fixed in the population (Figure 1), which did not support our prediction that the dominant allele would become fixed. Our hypothesis was supported, sine the bottleneck disrupted the equilibrium. The natural disaster selects causes new allele frequencies by pure chance. In the gene flow experiment, we saw that the frequency of each allele is changed with each migration event between the generations (Figure 2). This did not support our hypothesis that the two allele frequencies for the populations would converge to have similar frequencies. The Hardy-Weinberg requirement of no migration was violated by the exchanging of individuals between populations. None of the alleles became fixed in the population. However, in our simulation over 200 generations, we saw that allele p became fixed in most populations and disappeared in population 2 (Figure 6). Our bottleneck compared to that of other students in that ours was a less steady fixation. While our bottleneck took thirteen generations to become fixed, other students’ took only eight generations. Also, the recessive q allele was fixed in the population while the dominant p allele became fixed in another group’s