Two aligned sequences for the same gene differ by four subst

Two aligned sequences for the same gene differ by four substitutions, all transitions. Two more sequences for the same gene also differ by four substitutions, two transitions and two transversions.

Which pair of sequences has probably been evolving independently longer, and why do you think so?

Solution

First pair of sequences because Transitions are interchanges of two-ring purines (A to G) or of one-ring pyrimidines (C to T) they therefore involve bases of similar shape. Transition mutations are generated at higher frequency than transversions which is interchanges of purine for pyrimidine bases, which therefore involve exchange of one-ring and two-ring structures. Therefore transitions are less likely to result in amino acid substitutions and are therefore more likely to persist as silent substitutions in populations as single nucleotide polymorphisms (SNPs). So it will long time to make changes in amino acid sequences hence in the evolution in compare to the group having transversion mutation.