In population genetics, genetic drift is the random change in how common alleles are from one generation of seed to the next, caused by which plants happen to reproduce. In small populations it can lose alleles entirely or fix them by chance, regardless of whether they are useful.
In practice
Drift matters for seed lines. Keep a line going with two or three parents per generation and it drifts quickly: alleles vanish, variation shrinks, and the line can change type without any selection. Open-pollinated and heirloom lines stay true to their character only with enough parents each generation.
Growers also say "clone drift" for an old cut that seems to have changed. That is a different claim, and it is wrong.
Don't confuse with
- Selection: non-random change, driven by the breeder's choices.
- Somatic mutation: rare changes in a plant's own cells. They happen (Adamek et al. 2022), but a mutation does not mean a loss, and it is not drift.
- Topophysis: cuts from different parts of a plant behaving differently.
Myth check
House position: clones show zero genetic drift apart from pathogens. A cut that declines over years almost always carries a pathogen such as hop latent viroid, or suffers poor mother care. The GenetixBay founder keeps cuts 40+ years old and seed stock 50 to 70 years old with no decline. See hop latent viroid and viruses and Mythbusters.
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.Open-pollinated seed comes from a population left to cross freely among its own plants, without controlled pairs, which keeps a line's variation and type over generations.An heirloom is a seed line kept and passed down by growers for decades, usually outside its region of origin, preserving an older type rather than a recent hybrid.Topophysis is the tendency of cuttings to keep traits linked to the position on the mother plant they were taken from, so cuts from different parts can behave differently.HLVd, a small infectious RNA that spreads through sap and tools, causing stunting, brittle stems, small loose buds and reduced resin in cannabis; called dudding.The gene pool is the total set of alleles present in a population, cultivar group or species; a narrow gene pool limits what breeders can select from.A genetic bottleneck is a sharp drop in the number of breeding plants, after which the population carries only a fraction of its former genetic diversity.The founder effect is the loss of genetic diversity when a new population is started from a few individuals, so it carries only a sample of the source population's alleles.Somaclonal variation is genetic or epigenetic change that appears in plants regenerated from tissue culture, especially from callus, making them differ from the donor plant.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.A clone-only is a cultivar that exists only as cuttings from one original plant, with no seed line that reliably reproduces it.
