A study conducted at the University of Toronto (UT) has produced the world's
first chromosome map of cannabis, revealing the plant's evolutionary past
and points to its future as potential medicine. The researchers from UT's
Donnelly Centre found that THC and CBD, bioactive substances produced by
cannabis and sought by medical patients and recreational users, sprung to
life thanks to ancient colonization of the plant's genome by viruses.

The new map reveals how hemp and marijuana, which belong to the same species
Cannabis sativa, evolved as separate strains with distinct chemical
properties. Cannabis plants grown for drug use ("marijuana") are abundant in
psychoactive tetrahydrocannabinol, or THC, whereas hemp produces
cannabidiol, or CBD, popular of late for its medicinal potential.



The enzymes making THC and CBD are encoded by THCA and CBDA synthase genes,
respectively. Both are found on chromosome 6 of the 10 chromosomes the
cannabis genome is packaged into. There, the enzyme genes are surrounded by
vast swathes of garbled DNA which came from viruses that colonized the
genomes millions of years ago. This viral DNA, or retroelements as it is
known, made copies of itself that spread across the genome by jumping into
other sites in the host cell's DNA.

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