okay, I’ll have to test out your theory and see if I get the same 1:1 for all offspring 
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Ah shit. That was a typo. CBD dom x THC dom will yield all 1:1 progeny.
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Fun to test anyway; in de Meijer et al. 2003 he took a THC dom and CBD dom and ended up with a 1:2:1 segregation of chemotypes. Not sure about the THC:CBD ratios though. I don’t believe they were exact ratios but were sorted into; drug chemotypes: mixed chemotypes: hemp chemotypes.
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Yes, in simple examples like red and white make pink color in a flower this will work with a square. In more complicated examples where two allele may react as a combination, difference or average (such with percentages) or any one of these three based in the allele the square becomes much more difficult.
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In the deMeijer experimental crosses in that paper, all F1 had intermediate CBD/THC phenotypes (intermediate, type 2 plants):
The inheritance of chemical phenotype in Cannabis sativa L. (12586720 (1).pdf)
Etienne PM de Meijer, Manuela Bagatta, Andrea Carboni, Paola Crucitti, VM Cristiana Moliterni, Paolo Ranalli, Giuseppe Mandolino
Genetics 163 (1), 335-346, 2003
Four crosses were made between inbred Cannabis sativa plants with pure cannabidiol (CBD) and pure Δ-9-tetrahydrocannabinol (THC) chemotypes. All the plants belonging to the F1’s were analyzed by gas chromatography for cannabinoid composition and constantly found to have a mixed CBD-THC chemotype. Ten individual F1 plants were self-fertilized, and 10 inbred F2 offspring were collected and analyzed. In all cases, a segregation of the three chemotypes (pure CBD, mixed CBD-THC, and pure THC) fitting a 1:2:1 proportion was observed. The CBD/THC ratio was found to be significantly progeny specific and transmitted from each F1 to the F2’s derived from it. A model involving one locus, B , with two alleles, B D and B T, is proposed, with the two alleles being codominant. The mixed chemotypes are interpreted as due to the genotype B D/ B T at the B locus, while the pure-chemotype plants are due to homozygosity at the B locus (either B D/ B D or B T/ B T). It is suggested that such codominance is due to the codification by the two alleles for different isoforms of the same synthase, having different specificity for the conversion of the common precursor cannabigerol into CBD or THC, respectively. The F2 segregating groups were used in a bulk segregant analysis of the pooled DNAs for screening RAPD primers; three chemotype-associated markers are described, one of which has been transformed in a sequence-characterized amplified region (SCAR) marker and shows tight linkage to the chemotype and codominance.
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Yes, the part we are looking for is the F1 CBD:THC ratios? The same progeny as their parents? It says mixed and doesn’t go into ratios. Makes sense a self cross would be the same progeny as it’s parent for the F2’s. It also says the F2’s progeny matches their F1’s which would imply that F1’s had different ratios from the original cross.
I’ll try a test myself and see the ratios from the original cross
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So the parents of the F1’s are the squares, all the triangles are the F1’s. I don’t see a correlation between the levels and their parents.
In your example if P1 is 3.25% THC and 0% CBD, the second parent is 0% THC and 1.5% CBD. Are you saying all the offspring will be 3.25% THC and 1.5% CBD to match their parents.
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The F1 is the original cross.
All of the offspring in that graph are intermediate CBD:THC (slightly more CBD). The total potency varies, but the ratio is relatively consistent, with no high THC or high CBD plants in the F1, all are intermediate.
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The levels of THC and CBD can very greatly if you use two parents that have 20% of THC and CBD. Also in this small example some are 2:3, 3:5, 4:5 crosses, you may see 1:2 in a larger graph up to 20%. Then you’re going to have to grow a lot of plants to test to make sure you get what you’re looking for.
You would have to assume some testing was done to have perfect parents. With seed companies saying low THC or CBD and that the F1’s you receive are also stabilised.
I still think if you’re aiming for something specific it’s best to test, or get seeds that guarantee the ratio and levels you’re looking for.
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Here’s some reading on Mendel’s Laws and non-Mendelian genetics; this is why I don’t use Mendel’s Laws when referencing linked genes or co-dominance.
Co-dominance is a direct violation of the Law of Dominance. Although it could be possible the allele are incomplete rather than co-dominant. You’d see this in flowers that can have different shades of pink from red and white parents, to use a simple example to match my co-dominance example of pink flowers.
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Ok. My point is that a single-cross Punnet’s square, and simple, single gene inheritance can be used to predict progeny (for what can be treated as a single locus) for the cross in question. Codominance doesn’t affect the genotype ratios of a Punnet square, even if codominance violates a law of Mendle.
I honestly forgot Mendel didn’t understand codominance. I tend to think of nonmendelian as quantitative, extranuclear inheritance, and epigenetic type examples. Regardless you can pretend the “B-locus” is a single, codominant gene and that this “single locus” predominantly determines chemotype. Unless you are specifically searching for rare, intermediate recombinants, you can ignore them here.
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That’s why Mendel’s work was so revolutionary at the time. Everyone had the assumption that all inheritance was incomplete dominance, he was the first to see dominant and recessive traits. If he had seen examples of co-dominance or incomplete dominance in his experiments then he may never had come to his conclusions and followed the status quo I’m sure his theories may be applied to other areas as well.
At this point I don’t think anyone has a definitive answer, lots of theories.
There is definitely a gene linking with CBDA and THCA that can be observed. At least my observations are (then again I could be wrong):
THC + CBD <= 26%
High CBD strains at 25:1
High THC strains at 1:25
Equal ratios are <= 10%
Although in strains with THC + CBD < 26%, there could be other cannabinoids at play.
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