Selection is deciding which plants get to reproduce. In breeding it is deliberate (artificial selection): the breeder grows a population, judges it, and uses only the best plants as parents. Over generations, the alleles behind the chosen traits become more frequent.
In practice
Selection works on whatever the breeder measures, and only as fast as heritability allows. High-heritability traits (flowering time, chemotype, leaf shape) shift in a generation or two. Low-heritability traits (yield, potency percentage) need large populations, uniform conditions and repeated testing of clones or offspring.
Selection also works on both sexes. Choosing the female carefully and grabbing any male wastes half the opportunity. Breeders evaluate males by structure, vigour, smell of stems and early flowers, and above all by the offspring they produce.
Culling is the other half: removing every plant with intersex flowers, weak roots, poor pest resistance or off-types, whatever its other virtues.
Breeder's equation: R = h² × S. The response (R) equals narrow-sense heritability times the selection differential (S: how far the chosen parents are above the population average).
Don't confuse with
- Natural selection: survival in the wild or a field without a breeder choosing.
- A pheno hunt: one round of selection among seedlings.
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.Heritability is the share of a trait's variation within a population that is due to genetic differences rather than environment, on a scale from 0 to 1.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).In cannabis growing, a plant (usually female) that develops both pistillate and staminate flowers or anthers; botanists call it intersex or monoecious expression.Selection pressure is how strongly a breeder, or the environment, favours some plants over others, set by how few are kept and how demanding the criteria are.In grower slang, a pheno is one individual plant from a seed lot, usually numbered during a hunt, as in "the #4 pheno".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 pheno hunt is growing many seeds of one line side by side and evaluating them to select the best individual plants, which are then kept as clones.Male selection is the choice of which male plants become parents, judged by their vigour, structure, early aroma and above all by the quality of their offspring.A progeny test judges a parent by growing out and measuring its offspring, the most reliable way to know what a plant, especially a male, actually passes on.Stabilisation is breeding a seed line over several generations, with selection each time, until it reliably reproduces the chosen traits from seed.
