Question

The given DNA non‑template sequence (coding sequence) is transcribed from 3' to 5'. Use the sequence to determine the type of mutation and the type of base substitutions that apply to each scenario. Place only one statement for each scenario.

3' A T G A A G C G C T C A G T A 5'

A. A thymine substituted for nucleotide 6
B. A guanine substituted for nucleotide 11
C. A guanine substituted for nucleotide 15

1. missense and transition
2. nonsense and transition
3. missense and transversion

Answer 1

In scenario A, substituting thymine for the sixth nucleotide is a transition leading to a missense mutation. Scenario B, a transition at the eleventh nucleotide, typically results in a silent mutation. Scenario C, a transversion at the fifteenth nucleotide, results in a missense mutation.

Step-by-step explanation:

For scenario A, where a thymine is substituted for nucleotide 6, the original sequence would be G so replacing it with a T would be a transition mutation. This changes the amino acid coded by this codon, resulting in a missense mutation.

In scenario B, a guanine substituted for nucleotide 11, would also be a transition, because the original base is C and it's replaced with G, which does not change the amino acid due to the redundancy of the genetic code (silent mutation not listed as an option). Scenario C, a guanine replacing nucleotide 15 that originally was an A, is a transversion. Since this changes the resulting amino acid, it's considered a missense mutation.