Drosophila mauritiana and D.melanogaster diverged 2 million years ago.Between these species, 40 nucleotide differences have accumulated at a gene.At that same gene, D.mauritiana and D.simulans have accumulated 8 nucleotide differences.Assuming that a molecular clock is operating, the best estimate for the divergence time between D.mauritiana and D.simulans is _______ years ago.
A) 100,000
B) 200,000
C) 300,000
D) 400,000
E) 800,000

Question

Quizplus · Accepted Answer

Since D. mauritiana and D. melanogaster diverged 2 million years ago and have accumulated 40 nucleotide differences, we can assume a molecular clock rate of 20 nucleotide differences per million years. Using this rate, we can determine the divergence time between D. mauritiana and D. simulans by multiplying the difference in nucleotides (8) by the molecular clock rate (20) and dividing by 2 (since we are comparing two species): (8 x 20) / 2 = 80. This means that D. mauritiana and D. simulans diverged approximately 80 million years ago. However, we are only looking for the estimate in years, not millions of years, so we need to divide by 200 (the number of generations per year for Drosophila) to get our final answer: 80,000,000 / 200 = 400,000 years ago. Therefore, the best choice is D) 400,000.

Drosophila Mauritiana and D