Suppose three sibling species of frogs have the following DNA sequences at a portion of a gene:
Species 1: AGTCTAGATCGCGGTCG
Species 2: AGTCGATCGCGGACG
Species 3: TGTCTAGATCACGGTCG

Recall that the observed number of mutations can differ from the total number of actual substitutions that occurred in pairwise sequence comparisons.Which modification would align the three sequences so they could be used to make comparisons?

Question

Suppose three sibling species of frogs have the following DNA sequences at a portion of a gene: 
Species 1: AGTCTAGATCGCGGTCG
Species 2: AGTCGATCGCGGACG
Species 3: TGTCTAGATCACGGTCG

Recall that the observed number of mutations can differ from the total number of actual substitutions that occurred in pairwise sequence comparisons.Which modification would align the three sequences so they could be used to make comparisons?

Quizplus · Accepted Answer

To align the three sequences, we need to insert gaps in the sequences at the appropriate locations. 
In this case, we need to make sure that the length of all three sequences is the same. 
As we can see, Species 1 and Species 3 have the same length, but Species 2 is shorter by two nucleotides.
To align Species 2 with Species 1 and Species 3, we need to add two nucleotides in Species 2. 
Looking at the sequences, we can see that the first four nucleotides in Species 2 match with Species 1 and Species 3, so we should not insert any gaps there.
The fifth nucleotide in Species 2 is different from the other two species, so we need to insert a gap there. 
Thus, the correct modification is to add a gap representing two nucleotides to Species 2 at the fifth nucleotide position (Choice C).

Suppose Three Sibling Species of Frogs Have the Following DNA