Question

A segment of DNA has a base sequence
ATG ACG GAC AGA AAC
Which of the following represents frameshift mutation?
A) GTC ATG AGA GAC AC
B) ATG CAG GGA CGA AC
C) ATG CGG ACA GAA AC
D) CAT GAC GAA CGA AC

Answer 1

Point mutations are a class of mutations that describe a change in a single nucleotide of DNA, such as a substitution for another nucleotide, deletion of a nucleotide, or insertion of a single nucleotide into the DNA, resulting in DNA that differs from the normal or wild type gene.

Complete answer:
Option: (C) ATG CGG ACA GAA AC
is the correct answer to this question.
A mutation is a heritable alteration in the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA.
A frameshift mutation occurs when a nucleotide base is either inserted or deleted which shifts the reading frame in a forward or backward direction respectively.
If you carefully observe the reading frame in the question and the reading frame in Option : (3) you can find that a nucleotide base ‘A’ is deleted from the second triplet codon thus shifting the reading frame backwards. Thus, there is a backward frameshift mutation.
ATG ACG GAC AGA AAC (Question)
ATG CGG ACA GAA AC (Option C)

Additional information:
If one focuses on all other options – (A),(B) and (D) we can find that there are frameshift mutations but the reading frame is also changed which are suggestive of multiple point mutations. So, all other options are incorrect.

Note:
A frameshift mutation is a type of genetic mutation induced by indels in a DNA sequence that is not divisible by three nucleotides. The insertion or deletion of a codon might modify the reading frame, resulting in a completely different translation from the original due to the triplet structure of gene expression via codons.