A line breeds true for a trait when its offspring reliably show that trait, generation after generation. Genetically, every plant is homozygous for the relevant alleles, so there is nothing left to segregate. Mendel's pea lines were true-breeding before he crossed them.
In practice
True breeding is trait by trait. An inbred cannabis line may breed true for chemotype and flowering time and still vary for aroma or yield. A balanced 1:1 THC:CBD plant can never breed true from seed because its chemotype comes from being heterozygous; crossing two of them gives the 1:2:1 split.
Breeders test it with a grow-out of enough seed. If every plant in 30 or more matches the target for the trait, the line is very likely true-breeding for it. Clones are always true to type for every trait, because they are copies, not offspring.
Don't confuse with
- True to type (clone): a cutting matches its mother. In seed, "true to type" means the line breeds true.
- Uniformity: often a sign of true breeding, but an F1 of two inbred lines is uniform and still does not breed true in the next generation.
- Stable sex: a separate quality. True breeding for aroma says nothing about herm rate.
Line breeding is a mild form of inbreeding in which plants are mated within a family, often back towards one outstanding ancestor, to concentrate its traits while limiting inbreeding.A plant is homozygous at a locus when it carries two identical alleles there (AA or aa), so it passes the same allele to every offspring.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 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).A plant is heterozygous at a locus when it carries two different alleles there (Aa), so its offspring can inherit either one and segregate.F1 is the first generation of offspring from crossing two parents; if the parents are inbred and different, F1 plants are uniform and often show hybrid vigour.Inbreeding is mating between related plants, which raises homozygosity; an inbred line is the resulting population, measured by the inbreeding coefficient F.The herm threshold is GenetixBay's two-tier herm standard: a 10-plant screening grow with zero herms to be featured, then about 150 or more community-grown plants before a line can be Verified under 2% herm rate.An IBL (inbred line) is a seed line that has been inbred and selected over many generations until it breeds true for its main traits, giving uniform offspring.Stabilisation is breeding a seed line over several generations, with selection each time, until it reliably reproduces the chosen traits from seed.Uniformity is how alike the plants of one seed batch are for traits such as height, timing and chemistry; F1s of inbred parents and IBLs are most uniform.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.
