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1a. The divergence between Drosophila melanogaster and D. simulans at putatively neutral sites is 0.128 and the species are thought to have diverged 2.5 million years ago. What is the mutation rate per site per year? (2 marks)
D = 2 u t
U = D(2t)
u = 0.128/(2 x 2.5 x 10^6) = 2.56 x 10^-8
b. If Drosophila species typically go through 10 generations per year, what is the mutation rate per site per generation? (2 marks)
u = Dg/2t
Ug = (2.56×10^-8)/10 = 2.56 x 10^-9
c. Describe how you can more directly estimate the mutation rate. (2 marks)
d. Let us imagine that using the method described in (c) we estimate the mutation rate per site per generation in Drosophila melanogaster to be greater than that estimated using the phylogenetic method. Assuming the method in (c) is correct give two reasons for the discrepancy (e.g. the species might have diverged more recently than assumed; assuming a longer divergence time depresses the phylogenetic estimate) (4 marks)
2a. It is generally assumed that advantageous mutations occur infrequently. Explain why. (2 marks)
b. Imagine that we have three loci, of equal length and mutation rate; the first has only advantageous mutations, the second neutral and the third deleterious mutations. Rank them in order of expected diversity (greatest first). (2 marks
Neutral
Advantageous
Deleterious
Sample Solution
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