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Genetic Analysis of Marijuana Finds Little Evidence of Distinct Strains

Cannabis sativa and Cannabis indica look very different, but their DNA tells a different story. 

| 2 min read

Cannabis sativa and Cannabis indica look very different, but their DNA tells a different story. A new genetic analysis shows that the names given to different strains of marijuana have little to do with their genetic identity.

If you’re at all familiar with marijuana — for whatever reason — you probably know that there are many different strains, each having a unique effect on the user. The two main species grown for medicinal and recreational use are Cannabis indica and Cannabis sativa. The short, fat leaves of C. indica are known for providing a mild, relaxing kind of high, whereas the longer, thinner leaves of C. sativa supposedly give a more euphoric high. Marijuana growers often claim that their products contain certain percentages of each strain, and that the effects of the drug will correspond with their composition.

But a recent study by Canadian researchers indicates that there’s a lot of hazy misinformation floating around the world of Cannabis dealing. The group analyzed the DNA sequences of 81 marijuana samples and 43 samples of hemp, a related species used for fiber and food production. The marijuana and hemp samples had distinct genotypes, or genetic identities, not only for genes related to the production of the psychoactive THC, but throughout their genomes.

SEE ALSO: Yeast Engineered to Produce Cannabinoids

However, the differences between samples that had been described as either C. indica or C. sativa proved to be less straightforward. When the researchers compared samples that had been given identical names by their growers, they found that 35 percent of the time, samples were more genetically similar to samples with different names than to identical ones.

One glaring example featured in the paper is a strain called “Jamaican Lamb’s Bread,” which is universally described as a variety of C. sativa. In fact, the sample turned out to be nearly identical to a sample from Afghanistan that had been identified as C. indica. Basically, there was almost no correlation between the strain’s name and its actual genetic structure. While the two strains may have originated with distinct genetic sequences, rampant crossbreeding and misclassification over the plant’s long history of cultivation has blurred those lines.

The problem starts with the seed. Farmers of other crops generally assign a strain name only if they know for sure that the plant is a direct clone. For obvious reasons, marijuana farming is covert and less regulated, and the strains are named even if they’re grown from seeds of uncertain origin. This raises a huge issue for the medical application of marijuana because physicians recommend the alleged therapeutic effects of certain strains to match the specific needs of each patient.

The dearth of information on the genetic basis of different marijuana strains and their purported effects can be blamed on the continued controversy surrounding the drug and red tape prohibiting its acquisition for research. But as the medical community and society at large trends towards embracing marijuana use, the value of studies like this one that aim to clear the air and establish solid knowledge should not be underestimated.

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