Cannabis cultivars are often advertised as being 'Indica', 'Sativa', or some blend of these (even getting so specific as to claim something like 20% Indica / 80% Sativa). Cultivars are advertised this way as a result of the commonly held belief is that 'Indica' cultivars have relaxing effects, while 'Sativa' cultivars are more energizing and cerebral.
Unfortunately, inheritance does not work this way.
While I believe that the effects of different cultivars vary depending on cannabinoid (or other secondary metabolite) content, the truth is that the 'Indica'/'Sativa' dichotomy is little more than genetic hocus-pocus.
They say with every legend there is a grain of truth, so perhaps we will start with what MIGHT be true.
- It is possible that pure Indica and Sativa cultivars each have a distinct chemotype that also has unique effects.
- It is possible, depending on the inheritance of the chemotype, that an F1 hybrid made between a pure Indica and a pure Sativa would have a chemotype (and effect) intermediate between the two. In addition, a breeder could reliably claim that the hybrid was 50% Indica / 50% sativa.
But things fall apart after that. Any additional work with that 50/50 plant opens Pandora's box. Chromosomes segregate independently, and recombination between chromosomes may occur. If you cross two of the 50/50 plants you could theoretically get a pure 'Sativa', pure 'Indica', or anything in between. The only way to know the background of a given plant would be to test a lot of genetic markers, as was done by these researchers.
Look at part 'b' of this figure. The colored column shows the actual percentage of Sativa (red) genetic background as determined by molecular markers, vs the reported background in numbers. There is only a weak relationship between the advertised background and the actual background.
On a more alarming note, the same research found that in 1/3 of cases, cultivars with one name were most similar to some other named cultivar.... meaning that the consumer has little idea what they are purchasing based on name alone.
Furthermore, the genetic background is mostly irrelevant to the chemotype once the breeding process begins. What really matters are the specific genetic loci that control the chemotype. These loci are unknown in number and location, but could be inherited independently of the majority of the genetic 'background'. In other words, a savvy breeder could create a 99.99% 'Indica' background cultivar with a full 'Sativa' chemotype.
I would encourage consumers to pay attention to the results from analytical labs, and their own bodies, and avoid buying into simplistic genetic explanations.
Here is some more information on cannabis chemotypes for those interested in the subject.