Scientists unlock the genetic switch controlling cannabis chemistry

Scientists have finally cracked the genetic code behind cannabis chemistry. Researchers discovered that the "B locus"—a specific region in the cannabis genome—functions as a supergene that acts like a genetic switch, determining whether a plant produces high-CBD or high-THC chemotypes. This locus contains two tightly linked genes (THCAS and CBDAS) with suppressed recombination between them, which explains why the trait behaves like a simple on-off genetic switch despite being controlled by multiple genes. This finding solves a long-standing puzzle in cannabis biology: how plants can stably maintain distinct chemical profiles across generations while following simple Mendelian inheritance patterns.

The research reveals surprising genetic complexity within the B locus, including substantial structural variations, gene copy number differences, and large-scale DNA insertions and deletions across cannabis varieties. Scientists also functionally characterized three previously unknown enzymes in the cannabinoid oxidocyclase family, confirming that cannabinoid profiles are specifically determined by which enzyme (THCAS or CBDAS) is present and active. Additionally, researchers mapped the expression patterns of the berberine bridge enzyme family across plant tissues, including the glandular trichomes that produce cannabinoids.

These discoveries establish a fundamental framework for understanding cannabis genetics and have immediate practical implications. Breeders can now identify and select for specific chemotypes more precisely, potentially developing plants with optimized cannabinoid ratios for medical applications. The findings also illuminate how cannabis evolved its remarkable chemical diversity—a result of selective pressures that maintained distinct chemotypes rather than allowing them to blend together.