Two lineages from a common ancestor each accumulate one base change per million years. Their DNA sequences differ at 12 bases. Approximately when did the lineages diverge?
Answer and explanation
Correct answer: B. 6 million years ago
- Step 1: Both lineages change independently, so the number of differences accumulates at twice the rate of one lineage: 2 changes per million years.
- Step 2: Time since divergence = 12 / 2 = 6 million years.
Answer
6 million years ago.
Why not the others: 12 million treats only one lineage; 3 million halves the answer again; 24 million doubles the rate wrongly.
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