Question

Is each of the following mutations a transition, a transversion, an addition, or a deletion? The original DNA strand is 5′-GGACTAGATAC-3 ′ (Only the encoded DNA strand is shown.)

A. 5′-GAACTAGATAC-3 ′ B. 5′-GGACTAGAGAC-3 ′ C. 5′-GGACTAGTAC-3 ′ D. 5′-GGAGTAGATAC-3 ′

Answer 1

The original DNA sequence given is 5′-GGACTAGATAC-3 ′

A.

The mutated sequence is : 5′-GAACTAGATAC-3 ′

Here, the nucleotide at the second position in the original DNA sequence is 'G' and in the mutated sequence is 'A'. So, a purine nucleotide 'G' is changed into another purine nucleotide 'A'.

This type of mutation is called as 'transition' in which a purine (A, G) nucelotide is substituted by another purine nucleotide or a pyrimidine nucleotide (C,T) is changed into another pyrimidine.

B.

The given mutated DNA sequence is : 5′-GGACTAGAGAC-3 ′

Here, the Pyrimidine nucleotide 'T' at 9th position in the original sequence is changed to the purine nucleotide 'G' in the mutated sequence. This type of mutation is called 'transversion'. In transversion mutation, a pyrimidine nucleotide is substituted by a purine nucleotide or vice versa.

C.

The given mutated DNA sequence is : 5′-GGACTAGTAC-3′

It is a deletion mutation. The nucleotide 'A' at the 8th position of the original DNA got deleted to form this mutant DNA sequence.

D. The given mutated DNA sequence is : 5′-GGAGTAGATAC-3 ′

Here, in the mutated sequence purine nucleotide 'G' is present at the fourth position instead of the 'C' pyrimidine nucleotide as in the original sequence. This type of mutation is called as 'transversion'. In transversion mutation, a purine nucleotide is substituted by a pyrimidine nucleotide or vice versa.