Terpene Profiles: Written in Genetics, Locked In

What You Need to Know

Your strain’s smell is determined by which terpene synthase genes it expresses and at what level. Allen’s team at Steep Hill Labs mapped the entire terpene synthase gene family — 55 genes total — and profiled terpenes across 240 cultivars. The conclusion is straightforward: you can nudge terpene yields with environment, but you cannot rewrite the terpene recipe. The Cheese will smell like cheese. The Haze will smell like haze. That’s not limitation — that’s the foundation of selecting reliable genetics.

Understanding how terpenes are genetically determined, not environmentally modified, lets you make smarter breeding decisions, choose cultivars with precision, and stop wasting time on environment tweaks that won’t change the profile.

The Science

Allen’s study had two parts. First, they profiled terpene content across 240 cannabis cultivars using GC-MS analysis of flower samples bound for dispensaries in Washington state. Second, they used the recently available Jamaican Lion genome assembly to identify and characterise all terpene synthase (TPS) genes — the enzymes that actually build terpenes from precursor molecules.

Terpene diversity across cultivars: The average flower sample contained 11.2 detectable terpenes above 1% of total terpene content, with 5.4 terpenes above 5%. The dominant terpene (usually myrcene, caryophyllene, limonene, or terpinolene) averaged only 35% of the total. The top four terpenes comprised 72% of total content. This means terpene profiles are complex — it’s never just “one terpene” defining a strain, even if marketing says otherwise.

Correlated terpene pairs: This is the finding that reveals the enzyme-level control. β-caryophyllene and α-humulene showed an R² of 0.92 — almost perfectly correlated. That’s because TPS9, a single enzyme, produces both compounds at a roughly 3:1 ratio. D-limonene and camphene: R² = 0.92. α-terpineol and fenchol: R² = 0.85. When two terpenes are tightly correlated across hundreds of cultivars, it means they’re coming from the same enzyme. You can’t increase one without increasing the other, and you can’t change the ratio because the ratio is built into the enzyme’s active site.

The gene family: Allen identified 55 full-length TPS genes in the cannabis genome, classified into three subfamilies: TPS-a (21 sesquiterpene synthases), TPS-b (26 monoterpene synthases), and TPS-c (4 diterpene synthases). Only 12 had been functionally characterised before this study. RNA expression data from Purple Kush showed that just three genes (TPS1, TPS18, TPS5) dominated total TPS expression, with TPS1 (limonene synthase) being the most highly expressed overall.

Multi-product enzymes: Most cannabis TPS enzymes produce multiple terpene products from a single substrate. TPS5 produces β-myrcene as its primary product but also generates α-pinene. TPS33 produces both α-terpinene and γ-terpinene in roughly equal amounts. This multi-product nature is why terpene profiles are complex — a small number of highly expressed genes produce overlapping sets of compounds, and the total profile emerges from the combined output.

Root-specific TPS genes: Allen’s team discovered a cluster of four nearly identical TPS genes expressed specifically in roots, not flowers. These root monoterpene synthases have unknown products but may play a role in below-ground ecological interactions. This finding means the plant is making terpenes you never smell, in tissues you never harvest, for purposes that have nothing to do with your jar.

How To Apply This

• Choose your genetics for terpene profile, not your growing method. If you want a limonene-dominant flower, grow a cultivar with high TPS1 expression. If you want myrcene, find genetics that express TPS5 heavily. No amount of molasses, UV light, or temperature manipulation will convert a myrcene-dominant strain into a limonene-dominant one.

• Stop trusting “indica vs sativa” labels for terpene expectations. Allen’s data showed that terpene profiles cluster by cultivar, not by the indica/sativa dichotomy. Two “sativa” strains can have completely different terpene profiles, and a labelled “indica” can have the same profile as a labelled “sativa.” The names are marketing, not chemistry.

• Focus on what you can control: harvest timing and drying/curing conditions affect which terpenes are preserved in the final product, even if they can’t change which terpenes the plant makes. Monoterpenes (myrcene, limonene, pinene) are volatile and evaporate during aggressive drying. Low-and-slow drying preserves more of the profile the genetics built.

• If you’re selecting seeds or clones, request terpene test results from the breeder, not just THC percentages. Terpene data tells you more about what the flower will actually smell and taste like than any strain name or marketing description.

Seb’s Corner (Level 2+)

The genomic organisation of the TPS family is revealing. About half the genes exist in genomic arrays — clusters of closely related genes on the same chromosome, suggesting recent gene duplication events. The largest cluster contains 11 TPS-b genes spanning roughly a megabase, including the characterised limonene (TPS1), α-pinene (TPS2), β-myrcene (TPS3), and β-ocimene (TPS13) synthases. These genes share on average 66% amino acid identity, indicating they diversified from a common ancestor but have been under divergent selection for product specificity. The TPS5/TPS11 cluster is particularly interesting: TPS5 (the dominant myrcene synthase) shares 73% identity with four root-specific synthases (TPS11, TPS36, TPS37, TPS38), despite having completely different expression patterns and likely different products. This suggests that tissue-specific promoter evolution, not just coding sequence evolution, has been a major driver of terpene profile diversification. For breeders, the key implication is that terpene profile modification requires changes at the regulatory level (which genes are turned on, where, and when) as much as at the protein level (what each enzyme produces). This makes terpene breeding more complex than cannabinoid chemotype breeding, where a single genetic locus controls the THC:CBD ratio.

Watch Out For

• “Terpene-boosting” nutrients: Terpene precursors (GPP for monoterpenes, FPP for sesquiterpenes) are synthesised from primary metabolic intermediates — pyruvate, glyceraldehyde-3-phosphate, and acetyl-CoA. These are abundant in any healthy, well-fed plant. There’s no evidence that specific nutrient supplements increase terpene precursor supply beyond what normal nutrition provides. If a product claims to “boost terpenes,” ask for the peer-reviewed trial. It doesn’t exist.

• Environmental terpene modification myths: Temperature drops, UV light, stress techniques — none of these change the terpene profile set by genetics. They may nudge total terpene concentration slightly (the volume), but they don’t change the ratio (the EQ).

• Pheno hunting as genetic roulette: If you’re growing from seed (not clones), two phenotypes from the same cross can express different TPS gene combinations due to genetic segregation. That variation is genetic, not environmental. Once you find the pheno you want, clone it to preserve it.

• Strain name unreliability: Two “OG Kush” from different sources may have completely different terpene profiles. Names are marketing. Test results are chemistry.

Quiz

1. Allen’s team found that β-caryophyllene and α-humulene showed R² = 0.92 across cultivars. What does this correlation tell us?

• A) The grower successfully adjusted their environment to change one without the other
• B) Both terpenes come from the same enzyme (TPS9) at a roughly 3:1 ratio *
• C) These two terpenes have similar boiling points and evaporate together
• D) The cultivars were cross-bred, so they inherited both genes together

2. How many full-length terpene synthase (TPS) genes did Allen identify in the cannabis genome?

• A) 12
• B) 26
• C) 35
• D) 55 *

3. True or False: You can convert a myrcene-dominant strain into a limonene-dominant strain by lowering night temperatures and using UV light.

• False * (Explanation: Terpene profiles are set by which TPS genes are expressed; environment affects total terpene yield, not the gene expression pattern.)

4. Most cannabis terpene synthase enzymes produce:

• A) A single terpene product from a single substrate
• B) Multiple terpene products from a single substrate *
• C) One terpene product from multiple substrates
• D) The same product regardless of substrate

5. You’re evaluating two seed bank listings for the same strain name. Why should you prioritise terpene test data over strain names when comparing them?

• Terpene profiles cluster by cultivar genetics, not by strain name. Two plants labelled the same way can have completely different TPS expression patterns and therefore different actual profiles. Test data shows chemistry; names show marketing.

FAQ

If terpenes are genetic, why does the same clone smell slightly different between grows? The total terpene content (percentage by weight) can vary with light intensity, nutrient status, and environmental conditions — Rodriguez-Morrison (Module 2.1b) showed modest terpene increases at higher PPFD. But the profile — which terpenes are present and in what ratio — stays consistent because the enzyme ratios don’t change. Think of it as the volume knob vs. the equaliser: environment turns the total terpene volume up or down, but genetics sets the EQ.

What about “terpene-boosting” nutrients? Terpene precursors (GPP for monoterpenes, FPP for sesquiterpenes) are synthesised from primary metabolic intermediates — pyruvate, glyceraldehyde-3-phosphate, and acetyl-CoA. These are abundant in any healthy, well-fed plant. There’s no evidence that specific nutrient supplements increase terpene precursor supply beyond what normal nutrition provides. If a product claims to “boost terpenes,” ask for the peer-reviewed trial. It doesn’t exist.

My two phenos of the same strain smell completely different. Isn’t that environmental? No — that’s genetic variation within the seed population. Unless you’re growing from the same clone, two seeds from the same cross can express different TPS gene combinations due to genetic segregation. This is exactly why growers pheno-hunt: they’re looking for the individual plant whose TPS expression profile produces the smell they want. Once found, that phenotype is preserved through cloning.

Can terpene testing help me pick better genetics? Absolutely. A full terpene panel from a testing lab gives you an objective chemical fingerprint of a cultivar. Comparing panels across cultivars is far more informative than strain names, which are unreliable and inconsistently applied. Two “OG Kush” from different sources may have completely different terpene profiles.

Source

Allen KD, McKernan K, Pauli C, Roe J, Torres A and Gaudino R (2019). “Genomic Characterization of the Complete Terpene Synthase Gene Family from Cannabis sativa.” PLoS ONE 14(9):e0222363. doi: 10.1371/journal.pone.0222363. CC-BY 4.0.