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GATE 2026 BT – Question 43

Genetics, Cellular and Molecular Biology · Molecular Biology: Structure of genes and chromosomes, mutations and mutagenesis, regulation of gene expression · 2 marks · Multiple select

The RNA sequence below depicts the part of a 330 nucleotides long mRNA and it encodes the C-terminal portion of a protein.

5'-… … … AAC ACC ACG ACC CAU GUG GCG AGA CGG UAG-3'

A mutation was identified in this RNA denoted as 322A$\rightarrow$U. This nucleotide change is represented by which of the following class(es) of mutation?

  1. Missense mutation
  2. Non-sense mutation
  3. Transversion mutation
  4. Silent mutation

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Correct answer: (B) Non-sense mutation; (C) Transversion mutation

Explanation

The mRNA is 330 nucleotides long and ends with the stop codon UAG at positions 328-330. The codon before it, CGG, is at 325-327, and AGA is at 322-324. So position 322 is the first base of AGA, and A$\rightarrow$U changes AGA to UGA, a stop codon: a nonsense mutation. A purine (A) changed to a pyrimidine (U) is a transversion.