Lab 1- Evolution: Observing Genetic Drift Through Bead Simulation

Null Busters! 

(Lien Huynh-Phan, Ameena Romani, Dena Al-Mousawi)

    In the Genetic Drift and Natural Selection lab, we hypothesized that genetic drift changes allele frequencies due to genetic drift, and we predicted that if alleles were randomly selected, then the resulting composition of alleles would include: an increase in alleles that were present in the first generation, and a decrease in alleles that were present in fewer amounts. This pattern is created because the selection is random, and the alleles that were present in higher frequencies in the first generation would have a higher probability of getting chosen in the generations after.  

Figure 1. This graph above shows Population A represented by 4 types of beads, Red, Clear, Black, and White to simulate 4 different allele frequencies and their changes over the span of 10 generations. The allele frequency started out relatively close in amounts however the Red allele frequency decreased over time while the Clear allele frequency increased over the span. The White and Black alleles seemed to fluctuate as time passed.

Figure 2. This graph demonstrates the different frequencies of alleles represented by four types of beads: Red, Clear, Black, and White, throughout ten generations and random selection, also known as genetic drift. Overall, the White allele frequency increased over the generations while the Red allele decreased over time. The Clear and the Black allele frequencies fluctuated over the generations.

Population A Calculations

Alleles	Expected	Observed	O-E	(O-E)2	(O-E)2/E
Red	12	1	-11	121	10.08
Clear	13	20	7	49	3.77
Black	12	10	-2	4	0.33
White	13	19	6	36	2.77
DF=3	p-v=0.5				Total:16.95

Table 1. This table was used for calculating chi-square to see if our null hypothesis was supported or not. Because our degree of freedom is three, our critical number is 7.82. Our total is 16.95 which exceeds the critical number, rejecting our null hypothesis.

Population B Calculations

Alleles	Expected	Observed	O-E	(O-E)2	(O-E)2/E
Red	12	2	-11	121	9.31
Clear	12	10	-2	4	.33
Black	13	9	-4	16	1.23
White	12	29	17	289	24.08

Table 2. This table demonstrates the expected and the observed outcomes of the null hypothesis by using a chi-squared formula (x^2=sum of ((O-E)^2)/E) that serves to set a critical number- in this case, 7.82. If the critical number is exceeded, then the null hypothesis has been rejected and the data supports the alternative hypothesis.

Conclusion:

During this lab, we randomly selected beads to create the next generation. There was no natural selection present in this lab since we just randomly chose the beads and had no criteria for which beads we selected. Our hypothesis was supported because a genetic drift occurred. We know that it occurred because in both populations (shown above in figures 1 and 2) the frequency of the red bead decreased greatly while the other colors increased.

We found that the null hypothesis was rejected in population B because the critical number was 7.82, while our calculated chi-square total came to 34.95. Since 34.95 is larger than 7.82, the null hypothesis is rejected and the alternative hypothesis is supported. In population A, the null hypothesis was also rejected since our chi-squared total, 16.95, is higher than the critical number 7.82. Our hypothesis is then supported but this evidence is not sufficient enough to support our hypothesis that our results are caused genetic drift since this is a simulation.