Question

Mutations induced by 5-bromouracil are

• A. Transversional mutations
• B. Transitional mutations
• C. Frameshift mutations
• D. Backward mutations

Answer 1

The correct option is B Transitional mutations

The transition is the substitution of one type of base by other of its own type. Hence, purine is replaced with purine (adenine to guanine and vice versa) and pyrimidine is replaced with a pyrimidine (cytosine to thymine/uracil and vice versa) only. 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. The transition is the substitution of one type of base by other of its own type. Hence, purine is replaced with purine (adenine to guanine and vice versa) and pyrimidine is replaced with the pyrimidine (cytosine to thymine/uracil and vice versa) only. 5-bromouracil replace thymine with cytosine thereby, causes the transition mutation. Thus, the correct answer is option B.