A/ATwo copies of the common allele. Published research associates this genotype with typical sensitivity to trimethylamine, the compound that gives spoiled fish its smell — most people find it strong and unpleasant at low concentrations.
A/GOne copy of the variant allele. Published research associates this genotype with rating the fish odour as less intense, and with more difficulty naming it, than people carrying no copies. TAAR5 is the receptor that detects trimethylamine specifically, which is why a change in this one gene can alter this one smell without affecting others.
G/GTwo copies of the variant allele. This is a rare genotype. Published research associates carriage of this variant with reduced perceived intensity of the fish odour; people with it may find spoiled fish and similar smells markedly less offensive, or may not register the smell at all.
Reduced sensitivity to a spoilage odour is worth knowing about in the kitchen rather than the clinic: a smell that warns other people that fish has turned may not warn you. Judge freshness by date and appearance as well as by smell.
Source: Gisladottir et al. 2020, Current Biology — sequence variants in TAAR5 and other loci affect human odor perception and naming (PMID 33035477); replicated for fish odour identification in a 2025 meta-analysis (PMID 40593737).