Pleiotropy is when one gene influences several traits. Change the allele and you change all of them at once, whether you wanted to or not.
In practice
Flowering-time genes are a good cannabis example. Kurtz et al. (2023) showed that the dose of the autoflowering allele in triploid plants changed both flowering timing and plant height. Breeders working autos therefore see height and timing move together, and cannot fully separate them by selection.
Pleiotropy is one cause of correlated responses in breeding. Push hard for one trait and another drifts: a line selected only for fast finishing may lose yield; one selected only for potency may lose vigour. Good breeders track several traits at once for this reason and record what else changed.
Don't confuse with
- Linkage: two separate genes near each other, inherited together. Recombination can eventually break linkage; it cannot separate two effects of one gene.
- Epistasis: two genes interacting on one trait.
- Environment: a correlation between traits can also come from the room, such as a hot spot that speeds finishing and cuts yield.
A gene is a stretch of DNA that carries the instructions for one functional product, usually a protein such as an enzyme, and is the basic unit of inheritance.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 day-neutral cannabis plant that starts flowering by age, usually a few weeks after germination, regardless of light schedule; the trait is mainly recessive.A polyploid plant carries more than two full sets of chromosomes, such as a triploid (three) or tetraploid (four); in cannabis these are almost always bred deliberately.Linkage is the tendency of genes that sit close together on the same chromosome to be inherited together, rather than independently.Epistasis is an interaction between genes in which the effect of one gene depends on, or is masked by, alleles at another gene.Selection in breeding is choosing which plants become parents, so that alleles behind the chosen traits become more common in the next generation.A quantitative trait varies continuously (yield, height, flowering time, cannabinoid content) because it is controlled by many genes of small effect plus the environment.
