To determine whether the differences between the human and chimpanzee genome are a result of natural selection or mutation and drift, geneticists compare synonymous and nonsynonymous substitutions. Genes that have evolved because of selection should show what pattern?

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If a gene has evolved due to natural selection, then it should show fewer nonsynonymous substitutions (changes to the amino acid sequence) than synonymous substitutions (changes to the DNA sequence that do not affect the amino acid sequence). This is because nonsynonymous substitutions are often deleterious and therefore removed by selection, while synonymous substitutions are neutral and accumulate over time.

To Determine Whether the Differences Between the Human and Chimpanzee