Question

In a random DNA sequence, what is the lowest frequency of encountering a stop codon?

• A. 1 in 20
• B. 1 in 3
• C. 1 in 64
• D. 1 in 10

Answer 1

Answer: (A)

Genetic codes are triplet. So, the total number of codon $=64$. Out of these there is one start (coding for methionine) codon and three stop codons (i.e. do not code for any amino acid).
$\therefore$ Functional codon $=64-3=61$
$\therefore$ Frequency of encountering stop codon
$=\frac{3}{61}=\frac{1}{20}$ approx.