Genotype and phenotype in cannabis

TL;DR

• Genotype = fixed DNA; phenotype = visible outcome with environment.
• Light, nutrients, temperature and stress measurably alter phenotype.
• Same strain name, different grower = often different values.
• Clones reproduce genotype exactly; seeds (F1/F2) vary genetically.

What does genotype specifically control?

Genotype fixes the potential: which enzymes (e.g. THCA- or CBDA-synthase) a plant can produce, and in what ratio. It also fixes baseline growth traits such as photoperiodism or flower structure. Genotype does not change during a plant's life — environmental stress can switch genes on or off (epigenetics) without altering the underlying DNA sequence (Lynch 2016).

Why do lab values fluctuate despite identical genetics?

Cannabinoid and terpene contents are quantitative, environment-sensitive traits. Light intensity and spectrum, nitrogen fertilisation, harvest timing, drying and curing shift measured final values by several THC percentage points, or substantially in terpene profile — even from the same seed. Lab values on packaging are therefore a snapshot of one harvest, not a biological constant of the variety.

• Light spectrum & intensity
• Nitrogen/potassium fertilisation
• Harvest timing (trichome maturity)
• Drying and curing conditions

Clone vs seed: what reproducibility is realistic?

A clone is genetically identical to the mother plant — it reduces variability to environmental factors alone. Seeds from open pollination (F2 or later generations) instead carry recombined genes from both parents and can vary phenotypically considerably, even within the same seed packet. Commercially 'stable' strains are usually lines selected over multiple generations with reduced, but not zero, variance.

Epigenetics and the role of gene expression in cannabis

Epigenetics describes processes that regulate gene activity without altering the underlying DNA sequence. While the genotype of a cannabis plant remains completely rigid from germination to harvest, the epigenome acts as a kind of dynamic switch. Environmental factors such as temperature, light spectrum, or nutrient availability leave chemical marks on the DNA. These marks determine how efficiently certain genes are read and translated into proteins or enzymes, directly influencing the expression of the phenotype.

This phenotypic adaptability is an evolutionary survival mechanism of the plant. If a mother plant is exposed to unfavorable conditions over a long period, she can even pass these epigenetic adaptations on to her cuttings. For professional breeders, this means that even genetically identical clones can develop different characteristics over several generations if the microclimate is not kept absolutely constant. Understanding these mechanisms is therefore crucial for long-term quality assurance.

• Epigenetic markers control gene activity without altering the DNA sequence.
• Environmental stimuli such as cold or drought activate protective metabolic pathways.
• A molecular memory can transfer traits to subsequent generations.
• Stable cultivation conditions minimize undesirable epigenetic deviations.

Regulatory Relevance and Swiss Pilot Projects

In Switzerland, genotype and phenotype play a decisive role in compliance with statutory limits. Since the launch of the scientific pilot trials under Article 8b of the Narcotics Act under the supervision of the Federal Office of Public Health (FOPH), producers must provide strictly controlled cannabis products. Since the total THC content, calculated from THC and THCA multiplied by a factor of 0.877, must be below one percent for freely available cannabis, choosing the right phenotype is essential. An unforeseen phenotypic variation could lead to batches exceeding the legal limit and being classified as illegal narcotics.

Phenotypic stability is also of central importance for medical cannabis, which has been eligible for medical prescription without an FOPH exceptional licence since August 2022. To ensure reliable therapy, Swiss physicians require standardised flowers or extracts with precisely defined active ingredient concentrations. Deviations in the terpene or cannabinoid profile, caused by insufficiently stabilised phenotypes or fluctuating environmental conditions in the production facilities, jeopardise therapeutic reproducibility. Therefore, Swissmedic monitors compliance with strict quality guidelines during propagation and cultivation.

• A total THC limit of below one percent requires extremely stable CBD phenotypes.
• Swiss pilot trials use genetically tested clones to ensure constant THC levels.
• Medical cannabis requires GMP-compliant standardisation to prevent phenotypic deviations.
• Competent authorities such as the FOPH and Swissmedic demand seamless proof of biological stability.

Systematic Phenohunting in Professional Breeding

So-called phenohunting describes the systematic process of selecting the optimal phenotype for commercial propagation from a large number of seedlings. To do this, breeders often germinate hundreds of seeds of the same strain and cultivate them under identical conditions. During the vegetative and flowering phases, subtle differences in growth habit, internodal spacing, root vigour, and pest resistance are documented. The goal is to find the plant that best expresses the strain's genetic potential in the desired environment.

In addition to visual and structural characteristics, chemical analysis is of paramount importance. Only laboratory analyses of the mature flowers reveal which phenotypes exhibit the desired ratios of cannabinoids and terpenes. The selected elite phenotype is then maintained as a mother plant, from which clones are exclusively cut for production. This elaborate selection process ensures the long-term homogeneity of harvests and minimises the risk of crop failures due to genetic instabilities.

• Selection is based on vigour, structure, flowering time, and pest resistance.
• Laboratory analyses ensure the exact ratio of cannabinoids and terpenes.
• Mother plant preservation secures the preservation of the exact phenotype over years.
• Reduces production risks by eliminating genetically weak individuals.

Phenotypic plasticity under stress

Phenotypic plasticity describes the extent to which a plant can adapt its appearance and chemical composition in response to environmental changes. Cannabis possesses exceptionally high plasticity, which makes the plant extremely adaptable but difficult for growers to predict. Severe stress such as extreme temperature fluctuations, irregular light cycles, or nutrient deficiencies activates physiological emergency programmes. These manifest not only in reduced growth but often also in a drastic alteration of the secondary metabolism.

A well-known phenomenon of this plasticity is hermaphroditism, where actually female plants develop male flowers under stress to ensure self-pollination. The density of trichomes and the synthesis of protective substances such as THC or certain terpenes, which serve as natural UV and herbivore protection, also fluctuate greatly depending on the stress level. For controlled production, it is therefore essential to consistently minimise stress factors through automated climate control and standardised irrigation systems in order to keep the phenotype within the desired target range.

• High plasticity leads to unpredictable fluctuations in active ingredients under environmental stress.
• Hermaphroditism is an evolutionary survival strategy during phenotypic overload.
• Trichome formation and terpene synthesis serve as biological defence mechanisms against stressors.
• Precise climate control stabilises the phenotype and prevents loss of quality.

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