Question

Which of the mutagen causes frame shift mutation?

• A. 2-aminopurine
• B. Proflavine
• C. 5-bromouracil
• D. Methane sulphonates

Answer 1

The correct option is B Proflavine

2-aminopurine is a purine analogue that acts like adenine and forms two hydrogen bonds with thymine. But its enol form pair with cytosine which means that its keto form replaces adenine and its enol form replaces guanine thereby causing transition mutations which make option A incorrect. 5-bromouracil (5BU) is a pyrimidine analogue which acts just like thymine in DNA replication and binds to adenine. The presence of the bromine atom causes 5-bromouracil to tautomerize more readily than thymine does; the enol form of 5-bromouracil pairs with guanine and thereby causes transition which makes option C incorrect. Proflavin is an acridine dye that intercalates itself between base pairs of DNA chain thereby causing loss or gain of the single nucleotide. The gene mutations that alter the base sequence of the whole genetic frame from the point of the mutation are called frame shift mutations. Here the reading frame of the base sequence is shifted forward (due to insertion of one or more nucleotide base) or in the backward direction (due to deletion of one or more nucleotide base). Thus, proflavin causes frame shift mutation which makes option B correct. Methane sulphonate cause mutation by base substitution; it alkylates guanine into 7-alkyl guanine which pairs with thymine instead of cytosine thus producing base pair mistake during DNA replication which makes option D incorrect.