Genotyping is determining which alleles a plant carries at a set of DNA markers, usually SNPs or short repeats, from a small tissue sample. The result is a genetic fingerprint that can be compared between plants.
In practice
What genotyping can show:
- whether two cuts are the same genotype (identity) or close relatives;
- likely parentage, if the candidate parents were also tested;
- seedling sex and cannabinoid synthase type, with dedicated markers (Toth et al. 2020);
- broad ancestry and population structure (Sawler et al. 2015; Henry et al. 2020).
What it cannot show: a cultivar's name, its exact THC percentage, its flavour or its yield. Those depend on many genes plus how it is grown. A DNA report saying "70% indica" reflects the reference panel used, not a species.
Results are only as good as the database. Comparing a cut to a reference only proves something if the reference itself came from a documented source.
Don't confuse with
- Potency testing: chemistry of the dried flower, not DNA.
- Genome sequencing: reads almost the whole genome; genotyping reads chosen markers.
- Strain ID apps: guesses from photos or names, not DNA.
An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different.A SNP (single nucleotide polymorphism) is a position in the DNA where plants differ by one base letter; thousands of them form the markers used in cannabis genotyping.The genotype is the set of alleles a plant actually carries, either at one locus or across its whole genome, as opposed to the traits you can see.A seedling is a young cannabis plant from emergence of the cotyledons until it has several sets of true leaves, typically the first 2-3 weeks.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.Potency testing is laboratory measurement of a sample's cannabinoid content, normally by HPLC, reported as % w/w or mg/g for each cannabinoid plus calculated totals.The daily length of light versus dark; photoperiod cannabis flowers when nights grow long enough, rather than at a fixed age.Marker-assisted selection is choosing seedlings or parents by testing DNA markers linked to wanted traits, so plants can be selected before they flower.A clone-only is a cultivar that exists only as cuttings from one original plant, with no seed line that reliably reproduces it.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).
