# DBT JRF 2020 — Question 40

Exam: DBT JRF 2020 · Section: A · Topic: Molecular Biology · Difficulty: Easy

## Question

The genetic codon is a triplet and there are 64 codons. How many codons would be possible if the codon is a doublet?

## Options

- **A.** 8
- **B.** 64
- **C.** 24
- **D.** 16

## Answer

Option D

## Explanation

The genetic code uses triplet codons: $4^3 = 64$ possible codons from 4 bases. If instead codons were doublets: $4^2 = 16$ possible codons. This illustrates why a minimum triplet code was evolutionarily necessary — 16 doublet codons could not encode all 20 amino acids plus stop signals. The triplet code provides $4^3 = 64$ codons for 20 amino acids and 3 stop codons, resulting in degeneracy (redundancy) — multiple codons can encode the same amino acid (e.g. Leu has 6 codons, Trp has only 1).

Source: https://mypyqbuddy.com/questions/the-genetic-codon-is-a-triplet-and-there-6a05a8a02adafec47029320e