Question

Instead of 3, if it was 2 bases code for an amino acid, the degeneracy of codons coding for the same amino acid would have-
A. Increased
B. Decreased
C. Remained the same
D. Been uncertain

Answer 1

Hint: Degeneracy of the codons occur because there are more encodable amino acids than there are codons. It is the redundancy of the genetic code which is exhibited as the multiplicity of three-base pair codon combinations that specify an amino acid. It is the phenomenon where one amino acid is coded by more than one codon.

Complete Answer:
- The codons coding for an amino acid exhibit redundancy but are not ambiguous. There are 20 natural amino acids used as a building block for proteins. We have 4 nucleotides, for these 4 base pairs to form codons to code for the 20 amino acids, 64 possible combinations of codons are formed $({{4}^{3}}=64)$ and thus degeneracy of the codon is observed.
- Instead of 3, if 2 bases code for an amino acid, then the possible number of codons coding for the amino acids will be 16 $({{4}^{2}}=16)$. In this case, only 16 amino acids will be coded and the degeneracy observed will be decreased due to a lesser number of codons. Thus to code all the 20 amino acids, we have to look for the next larger number of bases i.e, 3. Therefore, some degeneracy will always exist.
- So, if 2 bases code for an amino acid then the degeneracy for an amino acid will be decreased.

Therefore, the correct option is B) Decreased.

Note: Degeneracy of the genetic code was identified by Lagerkvist. The genetic code is degenerate mainly in the third position. This position is a non-degenerate site and any mutation at it does not result in amino acid substitution.