Chemotype

Chemotype (Greek chēmeia + typos, "chemical form") is a taxonomic-chemical classification of cannabis based on ratios of principal cannabinoids, first systematized by Small & Beckstead (1973) and formalized by Small (1979) and de Meijer et al. (2003, Genetics 163:335–346). Five widely recognized chemotypes are distinguished. Type I is THC-dominant (THCA ≫ CBDA; genotype B^T/B^T), the drug type. Type II is mixed or intermediate (THCA ≈ CBDA, ratio ~0.5–3; heterozygous B^T/B^D). Type III is CBD-dominant (CBDA ≫ THCA; B^D/B^D), the fiber and hemp type. Type IV is CBG-dominant (Fournier et al. 1987; de Meijer & Hammond 2005), arising from a non-functional THCAS allele (B^0). Type V is effectively cannabinoid-free (Mandolino & Carboni 2004; de Meijer et al. 2009). The B-locus co-dominant allele model (de Meijer et al. 2003) explains Mendelian segregation of Types I–III. Chemotype is distinct from — and narrower than — chemovar, which integrates terpenoids. → See also: Chemovar, THC, CBD, CBG (Chemistry).