The chemotype ratio describes how a plant's cannabinoid output is split, almost always expressed as total THC to total CBD. Researchers use five broad classes: type I, THC-dominant; type II, mixed THC and CBD; type III, CBD-dominant; type IV, CBG-dominant; type V, almost no cannabinoids. The ratio is set mainly by the synthase genes, so it is highly heritable and stable within a clone.
In practice
A COA showing total THC 21% and total CBD 0.05% is type I (ratio over 100:1). One showing 7% THC and 9% CBD is type II (about 1:1.3). Breeders crossing types I and III expect type II F1s and a segregating F2. Seedling genotyping can predict the class early; the absolute percentage still depends on many other genes and the grow.
Don't confuse with
- Chemotype (genetics term): the overall chemical phenotype or class; the ratio is how it's measured.
- Terpene profile: aroma chemistry, separate from the cannabinoid ratio.
- Potency: total amount, independent of the ratio.
Myth check
Indica/sativa labels don't predict the chemotype ratio or terpene profile (house position, supported by Smith et al. 2022 and others). See chemotype inheritance.
A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.THC (Δ9-tetrahydrocannabinol) is the neutral, decarboxylated cannabinoid mainly responsible for cannabis's reported intoxicating effects; the living plant makes it almost entirely as THCA.CBD (cannabidiol) is a non-intoxicating neutral cannabinoid formed when CBDA decarboxylates; hemp-type and CBD-dominant cannabis make it mainly as CBDA in their trichomes.F1 is the first generation of offspring from crossing two parents; if the parents are inbred and different, F1 plants are uniform and often show hybrid vigour.Segregation is the separation of a plant's two alleles at each locus into different gametes, so offspring of a heterozygous parent vary in which allele they get.F2 is the second filial generation, made by crossing or selfing F1 plants; it shows the widest segregation, bringing back hidden recessives and new combinations.A chemotype is a plant's chemical phenotype, in cannabis usually its dominant cannabinoid class: THC-dominant (I), mixed (II), CBD-dominant (III), CBG-dominant (IV) or cannabinoid-free (V).A terpene profile is the measured mix of terpenes in a sample, reported as each compound's % w/w and the total, used to describe and compare cultivar aroma chemistry.THCA synthase is the trichome enzyme that converts CBGA into THCA; which alleles of its gene a plant carries largely decides whether it is THC-dominant.CBDA synthase is the trichome enzyme that converts CBGA into CBDA; it competes with THCA synthase, and its alleles largely decide whether a plant is CBD-dominant.CBGA (cannabigerolic acid) is the precursor cannabinoid that the plant converts into THCA, CBDA or CBCA, formed by joining olivetolic acid to geranyl pyrophosphate.
