... time,¹

It was still vastly more laborious than it is now.

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... substitutions.²

Ignoring, for the moment, the possibility that there may be selection on codon usage.

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... away.³

Think about what that means for association mapping. In organisms with a large effective population size, associations due to physical linkage may fall off very rapidly, meaning that you would have to have a very dense map to have a hope of finding associations.

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... neutral,⁴

And unlinked to sites that are under selection.

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