The human genetic code uses triplet codons from four nucleotides (A, C, G, T/U), yielding 64 possible combinations sufficient for 20 amino acids plus stop signals. If doublet, only 16 codons would form, insufficient for protein diversity. This CSIR NET-style question tests understanding of codon mathematics: 4² = 16.

Codon Calculation Basics

Codons are nucleotide sequences read by ribosomes during translation. With four nucleotides, possibilities scale exponentially by codon length: singlet (4¹ = 4), doublet (4² = 16), triplet (4³ = 64).

Doublet code limits to 16 codons (4 × 4), covering fewer than 20 amino acids, explaining nature’s triplet preference for redundancy and stop codons.

Why Triplet Over Doublet?

A doublet code yields 16 combinations (AA, AC, AG, AU, etc.), inadequate for 20 amino acids without overlap issues. Triplet provides 64, allowing degeneracy (multiple codons per amino acid) and three stop codons (UAA, UAG, UGA).

George Gamow proposed triplet in 1954, confirmed experimentally; doublet fails biological needs.

Question Solution

The answer is 16, as 4² = 16 codons possible theoretically from four nucleotides in doublet code. No options given, but common distractors include 4 (singlet), 64 (triplet), or 256 (quadruplet).

Option-like analysis (typical MCQ):

• 4 incorrect (singlet, too few)
• 16 correct (doublet)
• 32 invalid (no 4ⁿ=32)
• 64 triplet actual

Direct integer: 16.

CSIR NET Relevance

For exams, remember: codon number = 4ⁿ, where n=length; doublet=16 insufficient, triplet=64 degenerate/universal. Practice permutations for genetics units.