Each of the following answer choices compares a segment of dna from two related species that diverged from a common ancestor. assume a mutation rate of one mutation every 60 million years applies to all segments and that a mutation can happen only once at each position in a dna sequence. which pair of sequences shows that the two species diverged from their last common ancestor 60 million years ago?
gattcact and aactcaca

gcgcttat and acgtttgt

tattcgcg and tattgccg

tcacttaa and tcactcaa

i thought it was the last one, considering it was only 1 mutation. but it is wrong and i am unable to find the correct answer, could someone explain why the last one is wrong to me?