# DBT JRF 2022 — Question 49

Exam: DBT JRF 2022 · Section: B · Topic: Molecular Biology › Mutations & Reading Frame Shifts · Difficulty: Medium

## Question

Which one of the following types of mutations can lead to a major change in the encoded protein? A. Insertion of a single nucleotide near the end of the coding sequence. B. Removal of a single nucleotide from the beginning of the coding sequence. C. Deletion of three consecutive nucleotides of a codon in the middle of the coding sequence. D. Deletion of four consecutive nucleotides in the middle of the coding sequence.

## Options

- **A.** A, D
- **B.** B, D
- **C.** B, C
- **D.** A, E

## Answer

Option B

## Explanation

Frameshift mutations — major vs. minor changes: Frameshift mutations caused by insertions or deletions NOT in multiples of 3 nucleotides alter the reading frame for all codons downstream of the mutation. • Option B: Removing 1 nucleotide from the beginning (position 1) → frameshift affects the ENTIRE protein — major change. • Option D: Deleting 4 nucleotides (not a multiple of 3) from within the sequence → frameshift from that point onwards — major change downstream. Minor changes would be: • Silent mutations (same amino acid) • Conservative substitutions • Deletion of exactly 3 bp (removes one amino acid, rest of protein unaffected) Answer: B and D cause major changes (both cause frameshifts).

Source: https://mypyqbuddy.com/questions/which-one-of-the-following-types-of-mutations-6a104cd5920734408bc0c740