An allele is dominant when one copy is enough for its trait to show. In a heterozygous plant (Aa), the dominant allele A sets the phenotype and the recessive allele a is hidden. Dominance describes how two alleles at one locus interact; it says nothing about whether the trait is good, common or strong.
In practice
Dominance is why a cross can hide traits. Cross a plant carrying a dominant trait with one lacking it and every F1 may show the dominant version. The recessive allele is still there, carried silently, and returns in about a quarter of F2 plants (the 3:1 ratio).
Autoflowering is the classic cannabis example of the reverse case: the autoflowering trait at the Autoflower1 locus behaves as recessive, so an auto crossed to a photoperiod plant gives photoperiod F1s (Toth et al. 2022). Breeders then need an F2 or a backcross to recover autos.
Don't confuse with
- Codominant: both alleles show (THC and CBD synthase at the B locus). Not a case of one masking the other.
- Prevalent: a dominant allele can be rare in a population; dominance is not frequency.
- "Dominant" in strain marketing: "indica-dominant" is a shape label, not a genetic statement.
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 recessive allele only shows its effect when a plant carries two copies of it; in a single copy it is masked by a dominant allele and carried silently.A locus is the fixed position on a chromosome where a particular gene or DNA marker sits; the plural is loci.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.F2 is the second filial generation, made by crossing or selfing F1 plants; it shows the widest segregation, bringing back hidden recessives and new combinations.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.The daily length of light versus dark; photoperiod cannabis flowers when nights grow long enough, rather than at a fixed age.CBDA synthase is the trichome enzyme that converts CBGA into CBDA; it competes with THCA synthase, and its alleles largely decide whether a plant is CBD-dominant.Codominance is when both alleles at a locus show in a heterozygous plant, as with THCA and CBDA synthase, so a B_T/B_D plant makes both THC and CBD.A plant is heterozygous at a locus when it carries two different alleles there (Aa), so its offspring can inherit either one and segregate.A Punnett square is a grid that lists each parent's possible gametes along two sides to predict the expected genotype ratios among offspring of a cross.
