do you think the high thc genotype is a recessive gene combination?

[Betterhaff]

Thanks for the information IntelliGeneS and Sam. I wasn’t taking into consideration other factors that may affect cannabinoid quantities just more or less the mechanisms of synthesis. If the desired chemotype is not present wouldn’t the other phenotypical traits make little difference?

With modern drug cultivars the emphasis has been on selecting for THC which would tend to be easier because of its effects, breed to the ones that give the most. In the process CBD was more or less bred out, not necessarily by design, but as the sacrifice in creation of plants with higher THC content. Breeding for CBD is different, it really can’t be done properly without cannabinoid testing.

Betterhaff, is the info you posted from De Meijer's papers? The inheritance of chemical phenotype in Cannabis sativa L.?
-SamS

Probably but not directly, I have read the paper(s). I started looking for more information when the CBD thing started to make waves so I have read a lot of articles and information. Not sure what’s up to date and/or accurate, as I said I was just thinking out loud.

 

[Only Ornamental]

QTL = Quantitative Trait Loci.

It has been suggested that cannabinoid synthesis is controlled by 4 different loci and with at least 2 of these the functional alleles are co-dominant. I think it’s also suggested that these loci are monogenic.
...

QTL have nothing to do with these 4 loci .
A QTL is not part of Mendels 'dominant/recessive' system but the loci here are.
Common QTLs are hight or skin colour (in humans). How exactly they work is still under investigation.

I do think that high THC is in fact caused by several QTLs not only such affecting biosynthesis itself but also things for example Sam and others mentioned.

 

[IntelliGeneS]

If the desired chemotype is not present wouldn’t the other phenotypical traits make little difference?

Chemotype is just one aspect of phenotype (the chemical aspect). Phenotype doesn't just mean plant traits, it is all aspects of an individual resulting from the interaction of Genotype and Environment. Some people describe Phenotype as "what we see," which is misleading since most aspects of Phenotype are invisible to us normally. Phenotype is expressed mathematically as:

P = G + E + GxE + error

But you are mostly correct in that cannabinoid composition won't be changed much by number of buds or bud weight, for example. But some differences could arise from differences in genes controlling flower morphology, like proportion of leaf to flower tissue at bud sites or amount and location of trichome initiations (e.g. more trichomes on sweet leaves vs less). When taken together, amounts of tissues with different chemotype expressions (leaf with more CBG as a hypothetical) can impact overall harvested bud chemotype. This just illustrates the complexity of the systems we're talking about there are many others which are easy to miss considering (epidermis thickness, waxy layer presence and thickness, internal cellular structures/frequency/placement, amount of leaf crenelation or curl, stem thickness, growth density, internode length, and on and on).

 

[Betterhaff]

QTL have nothing to do with these 4 loci .

I was just defining the QTL acronym, not meaning that the 4 loci mentioned are. I also said (or thought) it was suggested that these sites are monogenic. Sorry for the confusion.

Chemotype is just one aspect of phenotype (the chemical aspect). Phenotype doesn't just mean plant traits, it is all aspects of an individual resulting from the interaction of Genotype and Environment.

You’re right, I didn’t phrase that properly but I think you understood what I was getting at.