Two diploid species of closely related frogs, which we will call species A and species B, were analyzed with regard to genes that encode an enzyme called hexokinase. Species A has two distinct copies of this gene: Al and A2. In other words, this diploid species is A1A1 A2A2. The other species has three copies of the hexokinase gene, which we will call B1, B2, and B3. A diploid individual of species B would be B1B1 B2B2 B3B3. These hexokinase genes from the two species were subjected to DNA sequencing, and the percentage of sequence identity was compared among these genes. The results are shown here.

If we assume that hexokinase genes were never lost in the evolution of these frog species, how many distinct hexokinase genes do you think there were in the most recent ancestor that preceded the divergence of these two species? Explain your answer. Also explain why species B has three distinct copies of this gene, whereas species A has only two.

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AI A2 BI B2 B3 Percentage of DNA Sequence Identity A2 62 100 91 49 92 AI 100 62 54 94 53 B1 54 91 100 67 90 B2 94 49 67 100 64 B3 53 92 90 64 100