A polyploid has more than two complete chromosome sets. In cannabis the relevant types are tetraploids (4n = 40), usually made by treating seedlings or tissue-culture shoots with chemicals that block cell division and double the chromosomes, and triploids (3n = 30), produced by crossing a tetraploid with a diploid.
In practice
Triploids are the main commercial interest. Their uneven chromosome number makes meiosis fail, so they are largely sterile and set very little seed even when pollen drifts in. That makes them attractive for outdoor and hemp crops near pollen sources. Kurtz et al. (2023) used triploids to show that the dose of the autoflowering allele changes flowering time and plant height.
Tetraploids are larger-celled and sometimes larger-flowered, but bigger plants do not automatically mean more cannabinoids. Claims of higher potency from polyploidy are not consistently supported. Polyploid lines also inherit in more complex ratios, so stabilising them is slower.
Don't confuse with
- Diploid: the normal two sets.
- Polyhybrid: a hybrid with many ancestors. Unrelated to chromosome number, despite the similar word.
- Mutation: polyploidy changes whole chromosome sets, not single genes.
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 diploid organism carries two complete sets of chromosomes, one from each parent; normal cannabis is diploid with 2n = 20.Hemp is cannabis grown for fibre, seed or other uses and, in many laws, defined as Cannabis sativa with no more than 0.3% THC by dry weight.A day-neutral cannabis plant that starts flowering by age, usually a few weeks after germination, regardless of light schedule; the trait is mainly recessive.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 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.Stabilisation is breeding a seed line over several generations, with selection each time, until it reliably reproduces the chosen traits from seed.A polyhybrid is a cultivar whose recent ancestry mixes many different lines, so its seed segregates widely and rarely breeds true.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.Tissue culture is growing small pieces of a plant on sterile nutrient gel in a sealed vessel, used to multiply, clean up and store cannabis genotypes.
