What hypothesis did Francis Crick propose regarding the genetic code?

Francis Crick proposed the wobble hypothesis to explain how the genetic code can be read with fewer transfer RNA molecules than possible codons. He presented the idea in 1966.

Messenger RNA is read in three-letter units called codons. Because four RNA bases can occupy each of three positions, there are 64 possible codons. Three are stop signals, leaving 61 sense codons for amino acids. Yet many organisms use fewer than 61 distinct tRNA types, because one tRNA can recognize more than one codon.

Crick’s hypothesis explains this economy by allowing less strict pairing at the third position of the codon, which pairs with the first position of a tRNA anticodon. The first two codon bases generally provide most of the specificity, while the third can sometimes form non-standard pairings. Inosine in an anticodon is a classic example of a base that can recognize multiple partners.

The wobble hypothesis is not the same as the central dogma. The central dogma describes the general flow of biological information, while wobble explains flexibility in codon–anticodon pairing during protein synthesis.