A gene is a stretch of DNA that codes for one functional product, usually a protein. In cannabis many of the genes breeders care about code for enzymes: THCA synthase, CBDA synthase and the terpene synthases that set aroma. Each gene sits at a fixed position on a chromosome, and a diploid plant carries two copies of it, one from each parent.
In practice
Growers use "gene" loosely to mean "the genetics" of a plant. Breeders use it precisely. When a breeder says "the CBD gene is codominant", they mean the CBDA synthase gene at one locus, whose two versions (alleles) both show in the plant. Most traits growers select for (yield, vigour, resin density, flowering time) are not one gene but many genes acting together, plus the environment.
Don't confuse with
- Allele: a version of a gene. "Gene" is the slot; "allele" is what fills it.
- Genetics: the whole inherited make-up of a plant, or the science. "Good genetics" means a good genotype, not one gene.
- Strain: a market name. It says nothing reliable about which genes a plant carries.
The stretch is the rapid increase in height in the first two to three weeks after switching to flower, when many cultivars grow 1.5 to 3 times taller.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.Terpenes are volatile hydrocarbon compounds built from five-carbon isoprene units; in cannabis they are made in the trichome heads and are a major part of aroma and flavour.A diploid organism carries two complete sets of chromosomes, one from each parent; normal cannabis is diploid with 2n = 20.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.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.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 locus is the fixed position on a chromosome where a particular gene or DNA marker sits; the plural is loci.A chromosome is one long DNA molecule packaged with proteins that carries many genes; cannabis normally has 10 pairs, nine autosome pairs plus an X/Y sex pair.A mutation is a change in a plant's DNA sequence, arising in seed or in one branch (a somatic mutation); mutations are rare and usually neutral.
