First Genetic Map of Cannabis Reveals Its Medical Potential
For the first time, scientists have created a genetic map of cannabis, revealing new possibilities for its use in medicine. Researchers from the University of Toronto discovered that tetrahydrocannabinol (THC) and cannabidiol (CBD)—the biologically active compounds produced by cannabis—originated due to ancient viral colonization of the plant’s genome. This finding is just one of many breakthroughs made possible by the long-awaited cannabis genome map, which details the location of genes on the plant’s chromosomes.
Among other discoveries, the researchers identified a gene responsible for producing cannabichromene (CBC), a lesser-known cannabinoid that can also be used similarly to cannabinol. The results of this work were published in the journal Genome Research.
“The chromosome map will become the main foundation for further research, which, despite the widespread use of cannabis, has lagged behind studies of other crops due to legal restrictions,” says study co-author Tim Hughes.
Differences Between Hemp and Marijuana
The new map shows how hemp and marijuana, both belonging to the species Cannabis sativa, have developed as separate strains with different chemical properties. Cannabis plants grown for drug production (marijuana) are rich in the psychoactive compound THC, while hemp produces cannabidiol (CBD), known for its medicinal potential. Some people use CBD for pain relief, and it is currently being tested as a treatment for epilepsy, schizophrenia, and Alzheimer’s disease.
Genetic Origins of THC and CBD
The enzymes that produce THC and CBD are encoded by the THCA synthase and CBDA synthase genes, respectively. These genes are located on the sixth chromosome out of the ten that make up the cannabis genome. The enzymes are surrounded by large regions of distorted DNA originating from viruses that colonized the genome millions of years ago. This viral DNA, known as retrotransposons, created copies of itself that spread throughout the genome by moving into the host cell’s DNA.
Researchers believe that duplication of early synthase genes and the expansion of retrotransposons caused cannabis to split into chemically distinct types. Humans later identified these differences by selecting plants based on their effects, such as high THC content.
The gene sequences for THCA and CBDA synthases are almost identical, supporting the idea that they originated from the same gene, which was duplicated millions of years ago. Over time, one or both gene copies were scrambled by retrotransposon invasion and, evolving in parallel, began to produce two different enzymes—CBDA synthase found in fiber-type hemp and THCA synthase in marijuana.
Future Research and Legalization
“Scientists are still limited by restrictions on studying this species, but legalization and the expected easing of strict research regulations will provide opportunities for further testing. Canada is currently leading the way in this area,” the researchers conclude.