A/ATwo copies of the common allele. Published research associates this genotype with being able to smell the sulfur compounds that appear in urine after eating asparagus.
A/GOne copy of the variant allele. Published research associates each copy of this allele with roughly 1.67 times higher odds of being unable to smell those compounds — a specific anosmia, meaning the sense of smell is normal for everything else.
G/GTwo copies of the variant allele. Published research associates this genotype with the highest likelihood of not smelling anything unusual in urine after eating asparagus. Everyone produces the compounds; this is about whether you can detect them.
Source: Eriksson et al. 2010, PLoS Genetics — web-based, participant-driven studies yield novel genetic associations for common traits (PMID 20585627); odds ratio 1.67 per G allele, p = 7 x 10^-24.