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What's the difference between rope and dope? It basically amounts to one critical gene, according to Canadian researchers who have mapped the genome of Cannabis sativa – the plant which is the source of both industrial-strength fibre and marijuana.

The gene produces an enzyme which, in turn, is responsible for the production of THCA, or tetrahydrocannabinolic acid, the precursor of the mind-altering ingredient that makes pot smokers feel high.

In marijuana the gene is switched on, but in hemp it's turned off, according to report the research team led by Jon Page at the University of Saskatchewan and Tim Hughes at the University of Toronto found.

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Dr. Page noted that marijuana and hemp are extremely similar in many respects. Thousands of years of human cultivation and selective breeding, however, have led to two distinct strains of the plant with very different psychoactive properties.

Their findings, published in the journal Genome Biology, illustrate how subtle genetic variations can have profound consequences in living organisms. Dr. Page noted "this is the first genome sequencing of a medicinal plant." Further study of the plant's genetic blueprint could spur the development of new pharmaceuticals products and may even help boost hemp production.

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