Zhang, Z.#, Wong, G.K. and Yu, J.*

In eLS. John Wiley & Sons, Ltd: Chichester, UK

Abstract：

A protein‐coding gene is composed of a series of nucleotide triplets – the codons – that encrypt not only the protein content but also the start and stop signals. There are 64 (43) codons in the canonical genetic code, which encode 20 amino acids with redundancy. Hence, there are synonymous codons that encode the same amino acids, and they are used at different frequencies among different species. The resultant codon‐usage biases reveal complex interplays of mutation and selection. Protein‐coding genes can be organised into families of similar function, structure and sequence, according to their shared evolutionary histories. Individual proteins are modularly constructed of domains, which are often rearranged on evolutionary timescales to create functionally novel proteins.