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Biology (Biological Sciences)
Michael Harrington

Biology 207 - Practice questions 10 - Population genetics Question 1 In a wild population of sneetches you notice that 2/3 of the sneetches have stars on their bellies and 1/3 do not. This phenotype is due to a single autosomal gene named B. a) If the Btar allele is dominant to the BNostar allele what are the allele frequencies in this population? Star Let p = frequency of the B allele Let q = frequency of the B Nostarallele q = 0.333 q = 0.577 p = 0.42 Star Nostar b) If the B allele is recessive to the B allele what are the allele frequencies in this population? Nostar Let p = frequency of the B allele Let q = frequency of the B Starallele q = 0.667 q = 0.817 p = 0.183 Note that in both cases the recessive allele was more prevalent in the population. There is no rule that the dominant allele has to be more prevalent. Question 2 Both of the populations of flowering plants I used in class were in HWE. Consider a third population. In this field there are 116 red, 211 pink, and 173 white plants. a) Is this population in HWE? No. We can determine this by calculating the frequency of the C allele (p = 2x116 + 211 / 1000 = W 0.443) and the C allele (q = 211 + 2x173 / 1000 = 0.557). Next we use these values of p and q to calculate the expected numbers of plants with p = C /C , 2pq = C /C , and q = W W C /C . For a population of 500 plants this would be 98 red, 247 pink, and 155 white. The final step is to compare our actual population to the population predicted by HWE using a chi-squared test. This test gives a p-value of 10.64 which is greater thdf=2of 5.991 so we reject the null hypothesis that this population is in HWE. b) Assuming random breeding, no selection, etc.; what will be the genotypic and phenotypic ratios in the offspring population? R R R W W W The frequencies would be 0.196 C /C red, 0.494 C /C pink, and 0.310 C /C white. If this population also consisted of 500 plants this would give us 98 red, 247 pink, and 155 white. c) Is the offspring population in HWE? Yes. One round of random mating is all it takes for the alleles of an autosomal gene to enter HWE. (We won't cover it in this course but it takes longer for X-linked alleles to reach HWE.) Question 3 Hemoglobin, the oxyg
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