Question

A eukaryotic gene, which does not normally undergo splicing, was exposed to benzopyrene, a known carcinogen and mutagen. Following exposure, the protein encoded by the gene was shorter than before exposure. Which of the following types of genetic rearrangements or mutations was likely introduced by the mutagen? (A) Silent mutation (B) Missense mutation (C) Nonsense mutation (D) Duplication

Short answer

The correct answer is (C) Nonsense mutation, as it introduces a premature stop codon into the gene sequence, resulting in a shorter protein after exposure to benzopyrene.

Step-by-step solution

Rule out mutations that don't alter protein length

In this problem, we're trying to figure out which type of mutation is responsible for the shorter protein. In order to do this, we first need to eliminate any mutations that don't affect the length of the protein: silent and missense mutations. Silent mutations don't alter the protein sequence, while missense mutations simply substitute one amino acid for another, without affecting the length of the protein.

Evaluate remaining possibilities

Now that we've eliminated silent and missense mutations, we need to consider the other possibilities: nonsense mutation and duplication. A nonsense mutation introduces a premature stop codon into the gene sequence, which would cause protein synthesis to terminate early, resulting in a shorter protein. Duplication, on the other hand, would cause an increase in the number of repeating units in the protein, which isn't consistent with a decrease in protein length.

Choose the correct mutation type

Based on our analysis in step 2, we can conclude that the mutation that caused the protein to become shorter after exposure to benzopyrene is a nonsense mutation, which introduces a premature stop codon into the gene sequence. This mutation type is also consistent with the effect of the mutagen, which is known to cause genetic rearrangements and mutations. So, the correct answer is (C) Nonsense mutation.