You buy a 10-pack of Blue Dream seeds. You pop all 10. You give them identical soil, identical light, identical nutrients. By week 6, you have 10 noticeably different plants — different heights, different leaf shapes, different smells, different growth rates.
This isn't a quality control problem. It's genetics working as intended. Each seed carries a unique combination of its parents' traits, and that combination determines the phenotype — the observable characteristics of the plant. Understanding this is the difference between growing whatever the seed gives you and intentionally selecting the best expression of a strain.
Genotype vs. phenotype
Genotype
The genotype is the plant's DNA — the complete set of genetic instructions it inherited from its parents. You can't see the genotype. It's the blueprint.
Every cannabis seed (from sexual reproduction) gets half its DNA from the mother and half from the father. Because each parent has their own mix of dominant and recessive alleles, every seed gets a different combination. Even siblings — seeds from the same cross — have different genotypes.
Phenotype
The phenotype is what you can see, smell, and measure: height, leaf shape, flower structure, terpene profile, potency, color, growth speed, resistance to pests and disease.
Phenotype = genotype + environment.
The genotype sets the range of possibilities. The environment determines where within that range the plant actually lands. A genotype with the potential for purple coloration will only express purple if nighttime temperatures drop below 60°F during flower. The genetics are there, but the environment triggers the expression.
Why seeds from the same pack differ
F1 hybrids
Most commercial cannabis seeds are F1 hybrids — the first generation cross between two different parent strains. F1 hybrids exhibit "hybrid vigor" (faster growth, higher yield), but they're genetically heterozygous — each seed carries different allele combinations from the two parents.
Think of it like siblings in a human family. Same parents, but each child gets a different shuffle of the deck. One might be tall with dark hair, another average height with light hair. Same genetics pool, different results.