In a hypothetical experiment, researchers sequence a gene from a colony of bacteria at various times in the history of the colony.In the common ancestor, the nucleotide at site 998 is A.After 1,500 generations, it changes to G.After 5,000 generations, it changes back to A.We can infer that a total of _______ substitution(s) have occurred.Without knowledge of the sample taken at 1,500 generations, we would have inferred that _______ substitution(s) had occurred.

Question

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The correct inference is that two substitutions have occurred: first from A to G, and then back from G to A. Without knowledge of the intermediate state at 1,500 generations, we would have inferred zero substitutions, as the initial and final states are the same.

In a Hypothetical Experiment, Researchers Sequence a Gene from a Colony