Lab #1: Population Genetics by Hannah Fairchild, Katie Rupp, Cammie Edwards, and Hart Kitsondhi

Lab #1: Population Genetics by Hannah Fairchild, Katie Rupp, Cammie Edwards, and Hart Kitsondhi

Part A. Distribution of Genes in a Population

Hypothesis: The allele frequency of the beans will be affected by, and therefore follow the genotypic ratios of Mendelian genetics.

Null Hypothesis: The genotypic ratio of the beans will not be affected by those of Mendelian genetics.

Prediction: If the properties of Mendelian genetics are applied based off of our hypothesis, then the genotypic ratios of the beans will be 25% homozygous white, 25% homozygous speckled, and 50% heterozygous.

Figure 1. In the figure above, we have graphed both the expected and observed allele frequencies of the homozygous white, homozygous speckled, and heterozygous genotypes as they are randomly paired.

Genotype	Expected Genotypic Ratio	Observed Genotypic Ratio	(O-E)2	(O-E)2E
Homozygous White	12.5	15	6.25	0.5
Homozygous Speckled	12.5	14	2.25	0.18
Heterozygous (White, Speckled)	25	21	16	0.64
Total	50	100	-	1.32

Table 1.Distribution of genes over a population in a gene pool represented by white and speckled beans. The expected counts were assumed prior to the distribution of the beans. As we recorded in the table, X2= chi-square, which is a value of 1.32.

Conclusion (Gene Pool A): After randomly selecting haploids from 100 white and speckled beans to form 50 diploids, we found in our population of 50 pairs that 15 of the pairs were homozygous white, making up 30% of the population, 14 pairs were homozygous speckled, making up 28%, and 21 pairs in the population were heterozygous, making up 42% of the population (Figure 1). The 28% and 30% of the heterozygous pairs present in the population were close to the prediction that both should be around 25% (Figure 1). 42% of the population being heterozygous pairs is 8% off from the predicted 50% of the population consisting of heterozygous pairs (Figure 1). This suggests that while Mendelian genetics are certainly feasible in a situation such as this one, the genotypic ratios will rarely be exactly as predicted, and, as the chi-square value shows, are not close enough to the prediction to be deemed accurate. Therefore, our prediction is not accurate. We calculated the chi-square value from our data to be 1.32, where it would have to be greater than or equal to a value of 5.99 in order to reject the null hypothesis. Given the rejection of the alternate hypothesis, we can conclude that Mendelian genetics had no effect on the allele frequencies, or genotypic ratio, in our gene pool.

Figure 2. In the figure above, we have graphed both the expected and observed allele frequencies of the homozygous white, homozygous speckled, and heterozygous genotypes as they were randomly paired.

Genotype	Expected Genotypic Ratio	Observed Genotypic Ratio	(O-E)2	(O-E)2E
Homozygous white	12.5	10	6.25	0.5
Homozygous speckled	12.5	10	6.25	0.5
Heterozygous (White, speckled)	25	30	25	1
Total	50	50	-	X2=2

Table 2. Distribution of genes over a population in a gene pool represented by white and speckled beans. The expected counts were assumed prior to the distribution of the beans. As we recorded in the table, X2= chi-square, which is a value of 2.

Critical Value(CV) = 5.99

Based off of the result,  2 < 5.99

Conclusion (Gene Pool B):

Overall, The distribution of the beans in the population was determined by the Mendelian law. According to our result (Table 1). The ratios between the expected and observed are slightly different but the chi-square was calculated to be 2, which is less than 5.99, the critical value. According to our calculations, the chi-square square value is less than the critical value, so we can conclude that the null hypothesis can not be rejected. Therefore, the deviation in the gene pool of beans was not significant enough to reject null hypothesis.

Part B. Genetic Drift or Natural Selection

Hypothesis: Genetic drift, or the random division of a population, affects the allele frequency (number of beans present) of both resulting populations in different ways over time.

Prediction: If population A and B are randomly separated by genetic drift, then their resulting allele frequencies in population A and B will be different from each other and continue to differ over time.

Null Hypothesis: Genetic drift does not cause the resulting allele frequencies to change over time, so each population’s change in allele frequencies will follow the assumptions of Hardy-Weinberg Equilibrium.

Figure 3. This figure shows the relationship between the number of alleles present in Population B over multiple generations. This graph depicts the loss of both the black and white alleles in the population. Additionally, the survival of the red and speckled alleles indicates their success in Population B’s region.

Figure 4. This figure shows the relationship between the number of alleles present in Population A over multiple generations. According to our data, all four alleles were still present in Population A after ten generations, though some were more frequent than others. The black allele was the least frequent in the population over the ten generations and the red allele was the most frequent over the majority of the ten generations.

Conclusion: Based on our calculations, the chi-squared value for population A was 6.42. In order to reject the null hypothesis, a value of at least 7.82 was required. Because 6.42 is less than 7.82, our chi-square value for population A suggested that the value is not significant enough for the change in allele frequencies to have a result of anything other than the mendelian genetics ratio (Figure 4). This suggests that no selection or genetic drift occured in Population A between the first and tenth generation because there was no significant deviation in allele frequencies from our original values (Figure 4). In contrast, our chi-square calculations for population B resulted in a value of 75.8. Because 75.8 is much greater than 7.82, the null hypothesis could be rejected. Therefore, population B rejects the idea that Hardy-Weinberg Equilibrium occured. This means that the significant changes in allele frequencies in population B likely resulted from a combination of non-random mating, natural selection, and genetic drift (Figure 3). The chi-squared value for Population B also indicates that the allele frequencies did not follow Mendelian genotypic ratios. After interpreting the allele frequencies for Population B, we determined that natural selection drove the success of the red and speckled alleles and caused the loss of the black and white alleles in the population (Figure 3). The data supports that the genotypes with red and speckled alleles were more successful in the region that Population B was relocated to after genetic drift occur (Figure 3). Based on these data, our hypothesis was supported because population A and population B experienced different changes in allele frequencies over 10 generations after the division from genetic drift occur.