Dominant and recessive cannabis traits — how to read a strain’s genetics.
03 June 2026 · 7 min read
Dominance seems simple: “a dominant gene beats a recessive one.” But the moment you move to real strains — purple color, autoflowering, aroma — it turns out that both those who think the topic is obvious and those who think it’s too complex get it wrong. Let’s break it down with concrete examples.
Diploid: why there are always two genes.
Cannabis, like humans and most animals, is a diploid organism. Each cell has 10 pairs of chromosomes: 9 pairs of autosomes and 1 sex pair. Every gene is present in two copies, one from each parent. During crossing the double set is split into halves (meiosis), and the offspring gets one half from each parent. That is why every trait is determined by two copies of a gene.
The notation convention.
A dominant trait is written with a capital letter (for example, photoperiod nature as “A”), a recessive one with the lowercase of the same letter (autoflowering as “a”). A dominant trait shows up even with just one copy in the pair; a recessive one only when both copies are recessive.
| Genotype | Notation | What shows up |
|---|---|---|
| Two dominant | AA | dominant trait |
| Dominant + recessive | Aa | dominant trait |
| Two recessive | aa | recessive trait |
The AA and aa states are called homozygous, Aa heterozygous. Play with the Punnett square: pick the parents’ genotypes and see how the offspring splits.
Why purple “beats” green.
Let’s cross a strain with purple buds and one with green buds. If all the offspring come out purple, then purple is dominant over green. The same mechanism applies to autoflowering: cross a photoperiod plant with an autoflower, and the whole first generation will be photoperiod. The autoflowering gene hasn’t gone anywhere — it’s in the genotype, it just doesn’t show up in the phenotype.
Why this matters to the grower and the buyer.
- Feminized and regular seeds behave differently: recessive traits may “pop up” in only some plants — this is normal segregation, not a defect.
- Stability ≠ uniformity: if a strain carries heterozygous pairs, some phenotypes will diverge. The more deeply a strain is stabilized, the smaller the spread.
- Aroma can be recessive: some of the most interesting terpene profiles are recessive, and they are harder to lock in.
Questions and answers.
What is a homozygous strain in plain terms?
A plant whose two copies of the gene in question are identical (AA or aa). Such strains produce uniform offspring. Landraces and IBLs are close to homozygosity, but almost never reach it 100%.
Can autoflowering be dominant?
Practically never. Autoflowering is a recessive trait, and a dominant version of it has yet to be found.
Why do plants from a single seed pack turn out different?
Because the strain carries heterozygous gene pairs, and when they segregate (Mendel’s second law) part of the offspring shows recessive traits. This is a law of nature, not a seed defect.