: the biochemical basis of heredity consisting of codons in DNA and RNA that determine the specific amino acid sequence in proteins and that appear to be uniform for all known forms of life
Sequence of nucleotides in DNA and RNA that determines the amino acid sequence of proteins. A messenger RNA molecule synthesized from the DNA directs the synthesis of the protein. Three adjacent nucleotides constitute a unit known as a codon; each codon codes for a single amino acid. There are 64 possible codons, 61 of which specify the 20 amino acids that make up proteins. Because most of the 20 amino acids are coded for by more than one codon, the code is called degenerate. Once thought to be identical in all forms of life, the genetic code has been found to vary slightly in certain organisms and in the mitochondria of some eukaryotes.