While the genome of the cannabis plant was sequenced back in 2011, researchers have struggled to isolate the genes responsible for producing the plant's two most prominent chemicals. Until now. A joint Canadian-US effort has identified the genes that produce THC (the chemical in marijuana that gets people high) and CBD (the compound most well known for its medicinal applications).
The main obstacle in the way of finding these genes earlier was the abundance of what researchers call 'junk DNA.' This is genetic information that has been dumped into the genome of marijuana by viruses over years of evolution. In fact, somewhere between 70 and 75 percent of the DNA of marijuana and hemp plants is derived from these viral sources.
"You can only manipulate a gene when you know where it is located," said Harm van Bakel - one of the study's contributors, who is also a genomic expert at the Icahn School of Medicine at Mount Sinai in New York. "And you also need to know something about the rest of the sequencing in the genome so that you can uniquely target the gene of interest and not be sidetracked by…other things that look similar," Bakel told told The Toronto Star.
But, not only did this mass of viral DNA keep the THC and CBD genes out of sight from researchers, it also likely contributed to their development. Exposing cellular mechanisms to viral DNA can cause mistakes that lead to genetic changes in plants like cannabis. These 'mistakes' are "almost certainly" what has promoted the development of marijuana's THC and CBD genes, according to Tim Hughes—a molecular geneticist at the University of Toronto's Donnelly Centre for Cellular and Biomolecular Research.
The discovery of the genes will make it much easier to grow weed with specific levels of the two primary compounds of cannabis. It also enables researchers to move on to figuring out which genes are responsible for giving different strains their signature taste and smell.