Historical milestone in molecular biology: in which year were the assignments of the genetic code essentially completed (codon → amino acid mapping established)?

Introduction / Context:
The genetic code links 64 codons to 20 amino acids and stop signals. Decoding this mapping enabled modern molecular biology, synthetic biology, and biotechnology. The work was a culmination of biochemical and genetic experiments in the 1960s.

Given Data / Assumptions:

• Poly(U) and related homopolymer experiments (early 1960s) initiated codon assignments.
• Triplet binding assays and defined repeating polymers refined the code.
• Final assignments were in place by the mid-1960s.

Concept / Approach:
Marshall Nirenberg, Har Gobind Khorana, and colleagues determined most codon assignments by 1966 using in vitro translation and synthetic RNAs. The Nobel Prize in Physiology or Medicine was awarded in 1968 for these discoveries, but the practical completion date of the code table is 1966.

Step-by-Step Solution:
Recall timeline: initial UUU→Phe (1961), expansion through early 1960s.By 1966, codon assignments were essentially complete.Nobel recognition followed in 1968, validating 1966 as the year of completion.

Verification / Alternative check:
Historical reviews and primary literature place the finishing assignments around 1966; textbooks consistently cite this date for the completed code.

Why Other Options Are Wrong:

• 1952/1958: predate the era of in vitro translation decoding.
• 1968: Nobel year, not when the code was completed.
• 1972: long after completion.

Common Pitfalls:
Confusing the Nobel award year with the experimental completion year; they are closely spaced but distinct milestones.

Final Answer:
1966