Genetic code

Definition

The set of nucleotide triplets (codons) that specifies which amino acid is added during protein synthesis, or signals translation termination. The code is read in mRNA by ribosomes using tRNA anticodons, with most organisms sharing a nearly universal code of 64 codons mapping to 20 proteinogenic amino acids and three stop signals. In arthropods, the code enables comparative phylogenomics; for example, mitochondrial genomes of insects and arachnids show a derived variant where AGA and AGG code for serine rather than arginine, and TGA codes for tryptophan rather than serving as a stop codon—diagnostic features used in molecular systematics.

Etymology

From 'genetic' (relating to heredity) + 'code' (system of symbols for communication), coined in the 1950s as the molecular basis of inheritance was being deciphered.

Example

In the honey bee Apis mellifera, the nuclear genetic code follows the standard pattern where the codon AUG initiates translation and codes for methionine, while the mitochondrial genome uses the invertebrate mitochondrial code variant with altered codon assignments that help distinguish bee lineages in phylogenetic studies.

Related Terms

• Codon
• Anticodon
• mRNA
• tRNA
• Ribosome
• translation
• mitochondrial DNA
• phylogenomics
• molecular systematics

Usage Notes

Distinguish 'genetic code' (the universal or variant translation rules) from 'genetic sequence' or 'genome' (the actual nucleotide content of an organism). Arthropod researchers must specify whether nuclear or mitochondrial genetic code applies, as mitochondrial codes differ among phyla and even among some arthropod groups. The term is sometimes misused in popular writing to mean 'genetic information' generally; in technical contexts, reserve it for the codon-amino acid correspondence rules.