Cannabis Genetics and Chemical Profile: What the Genome Evidence Shows

By Cannible Editorial

2026-08-08

Cannabis genetics can help explain why plants differ in cannabinoid and terpene chemistry: cannabinoid synthase genes are associated with CBD and THC chemotypes, while variation in a diverse terpene synthase gene family contributes to terpene profiles. That relationship is about plant chemistry, not a deterministic prediction of the subjective effect a consumer will feel. 1 2 3 4

This is plant-science information about cannabis genomes, genes, and chemical profiles. It is not human clinical evidence or health guidance.

What the genome evidence can establish

Genome studies connect particular genetic features with chemical traits, but the available evidence also has important technical limits. Cannabis genome assemblies have been described as incomplete, with missing or unmapped regions and limited representation of centromeres, satellite sequences, and ribosomal DNA. Those gaps can make it harder to identify complete, partial, or pseudogenized gene copies accurately. 5

One report estimated haploid genome size by flow cytometry at 818 Mb in female plants and 843 Mb in male plants. Separately, researchers generated a comprehensive draft genome assembly of approximately 900 Mb from the Cannbio-2 medicinal cannabis strain, which produces a balanced CBD-to-THC ratio. The approximately 900 Mb figure refers to that assembly and should not be substituted for the flow-cytometry estimates. 6

Cannabinoid chemotype and inheritance

Crosses between plants with pure CBD and pure THC chemotypes produced F1 plants with mixed CBD-THC chemistry. Self-fertilized F1 plants then produced F2 offspring segregating into pure CBD, mixed CBD-THC, and pure THC chemotypes in a 1:2:1 proportion. In that study, the CBD-to-THC ratio was progeny-specific and transmitted from each F1 plant to its F2 offspring. 2

The proposed explanation was a codominant locus with two alleles: one associated with CBD production and one with THC production. The mixed chemotype was interpreted as carrying both alleles, while pure chemotypes were associated with two copies of one allele. The proposed mechanism was that the alleles encode different synthase isoforms with different specificities for converting the shared precursor cannabigerol into CBD or THC. 2

More recent genome work gives this inheritance model additional genomic context. Cannabinoid synthase paralogs occur in tandem arrays on chromosome 7, and a CBD-type cultivar was found to carry hemp-introgressed CBDAS while lacking a complete THCAS sequence. Only CBDAS was expressed in that CBD-type cultivar, whereas both CBDAS and THCAS were expressed in a cultivar with an intermediate THC-to-CBD ratio. Variation at cannabinoid synthase loci may affect the THC-to-CBD ratio, while differences in overall cannabinoid potency were also associated with other chromosomes. 1

How terpene biosynthesis works in the plant

Cannabis terpene biosynthesis occurs in trichomes and uses the MEP and MVA pathways to produce substrates for terpene synthases. Glandular trichomes are especially abundant on the surface of female inflorescences, where terpene-rich resin accumulates. Transcripts associated with terpene biosynthesis are highly expressed in trichomes compared with non-resin-producing tissues. 7 8

Terpene synthases form a large and diverse gene family. One analysis described 55 terpene synthases with genomic context and tissue-specific expression, including root-specific monoterpene synthases. Another analysis of five cultivars and the Purple Kush reference genome identified 33 different CsTPS genes, including 19 complete CsTPS gene models in Purple Kush and three cannabis-specific phylogenetic clades. Thirteen of the characterized CsTPS genes had not previously been characterized and collectively explained a diverse range of cannabis terpenes. 4 3

Trichome transcriptome work in the hemp variety Finola identified terpene-biosynthesis sequences from multiple stages of the pathway and nine CsTPS genes in two subfamilies. Functionally characterized enzymes produced mono- and sesquiterpenes that included beta-myrcene, beta-ocimene, limonene, alpha-pinene, beta-caryophyllene, and alpha-humulene. 8

Genetic contribution to terpene profiles

The evidence supports a genetic contribution to terpene variation, but not a single-gene explanation for every profile. Five cultivars showed differences in CsTPS gene-family structure and differential expression of terpenoid and cannabinoid pathway genes. In a separate study, three genotypes collected at three maturity stages had different terpene profiles and distinct transcriptional patterns for terpene synthases. 3 7

The variation can occur even among plants carrying the same cultivar label. Plants grown from 32 seed sources showed large differences both between sets labeled as different cultivars and within sets labeled as the same cultivar. The researchers also identified a lack of metabolic characterization and sometimes incorrect cultivar labeling as problems in the cannabis industry. 3

Accordingly, a cultivar or strain name should not be treated as a guaranteed chemical specification. The reported within-label variation means that laboratory measurement of the particular plant or product is more informative than the name alone for determining its terpene profile. 3

Developmental stage, environment, and consumer experience

The terpene study described above compared three genotypes at three stages of maturity and found genotype-linked profile differences and distinct gene-expression patterns. That addresses developmental sampling, but the supplied evidence does not establish how a controlled environmental condition or cultivation practice changes a terpene or cannabinoid profile. No broader environmental or cultivation conclusion should be drawn from these genome findings alone. 7

Finally, genotype and chemotype are not the same as a consumer's experience. The evidence supports associations between genetic variation and measured cannabinoid or terpene chemistry, but it does not establish a deterministic link from a cannabis genotype, cultivar label, or chemical profile to an individual's subjective response. 1 2 3 4