According to the genetic code, the cell would need tRNAs with 61 different anticodons to complement the available 61 codons. However, due to the degeneracy of the genetic code, the third base is less discriminatory for the amino acid than the other two bases. This third position in the codon is referred to as the wobble position. At this position Us and Cs may be read by a G in the anticodon. Similarly, As and Gs may be read by a U or y (pseudouridine) in the anticodon.

The tRNAs also contain a series of unusual modified nucleotides. One of these nucleotides is inosine (I). If the tRNA contains an I in the anticodon at the wobble position, this tRNA may read codons having As, Us or Cs in the third position.