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How Ancient Viruses Gave Us Marijuana As We Know It Today

The two most well-known compounds in marijuana—THC and CBD—are the products of genetic mischief at the hands of ancient viruses, according to a recent study.

A team of researchers created the world’s first cannabis chromosome map, revealing how, millions of years ago, viruses colonized one of marijuana’s 10 chromosomes, where enzyme genes that produce THC and CBD exist. One or both of those genes was overwhelmed by DNA maligned by the viruses, and that viral DNA eventually spread throughout the cannabis genome.

There’s a lot of science to take in, but the idea is that through this mutative process, cannabis split into chemically different plant types: hemp, which contains mostly CBD, and marijuana, which has higher concentrations of THC. Human selection took over at that point and the respective plants evolved into what we have today.

The enzymes are still virtually identical at the DNA level, so it’s been unclear up to this point whether there were separate genes or two versions of the same gene that produced the enzymes. Part of the reason that question has confounded researchers is that marijuana and hemp contain both THC and CBD in different concentrations.

The study, published in the journal Genome Research, showed that there are, in fact, two separate genes involved in that process. That means it’s possible to separate them and cultivate cannabis without THC, for example.

“Mainstream science has still not done enough because of research restrictions,” Jonathan Page, who collaborated on the cannabis chromosome map, said in a press release. “Legalization and looming ease of research regulation really provide for opportunities for more research to be done. And Canada is leading the way.”

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