Species A and B have fewer differences between DNA sequences means that fewer mutations occurred. It is likely due to sequence homo-logy.
A mutation is any alteration in the nucleotide (DNA) sequence of the genome of a particular organism.
The linear order of nucleotides and their differences (mutations) can be used to infer homo-logy between two species.
In this case, there are only two different nucleotides in these sequences, thereby sequence homo-logy indicates a likely common origin.
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