Adding to and bookmarking this thread, but I love the truth and personal evolution that OG promotes!!!
For those looking to really dig into genetics breeding you should start out with the understanding that almost all of what we're growing and breeding with are not F1's & not polyhybrids, but are actually multi-polyhybrids. This definitely complicates things, but not so much that we can't still figure them out and stabilize them.
Sometimes we cross 2 strains and in their offspring generation we find out that the desired trait is recessive, but we only get dominant phenotypes and then in F2, we discover that we’re still stuck with those same dominant phenotypes.
Most people assume that F2 brings about 75% Dominant and 25% recessive. This is often believed to work in all F2's because of Mendel genetics "face value" teaching. However they forget that Mendel used a 100% stable Purple flower (P1) crossed to a 100% stable white flower (P2) which is then cultivated in very large numbers through each filial generation.
Focusing only on the F2 generation we would get these results:
Pp x Pp (Big P is Dominant and p is recessive desired phenotype).
We get PP, Pp, Pp, pp with this combination, everywhere there is a big P the cross will have Dominant phenotype, in this case green buds. 75% green and 25% purple.
Mendel genetics states:
* P1+P2=F1 (filial cross)
* F1=mostly Dominant traits
* F1+F1=F2 is where recessive genes show.
* So you can think F1= 100% Green, F2= 75% Green and 25% Purple
However with a collection of F2 plants showing only the Dominant phenotype of Green the issue can become more complex. The most time conserving way to deal with this issue is to grow more F2 generation seeds until you find a purple one. However, sometimes that isn't possible, because of a shortage of F2 seeds or lack of the needed space for larger plant sifting, and so further generations of plants will need to be bred in order to find the purple phenotype. There are 3 potential beginning genotype combinations we could be starting with in the F2 generation:
PP x PP, Pp x Pp, or PP x Pp
P = Green buds, p= Purple buds
Combinations of this will be PP, Pp, pp
100% Dominant traits P= Green in 11 of 12 plants with purple only appearing in one plant.
So, P1+P2=F1, then F1+F1=F2 would be unlikely to create the desired purple in a low number of plants in this situation, contrary to the way it did in Mendel's project.
Here is the solution to this problem:
P1 (Green) +P2 (Purple)=F1
PP (P1) +pp (P2) = Pp,Pp,Pp,Pp (F1)
Pp (F1) + pp (P2) = Pp,Pp,pp,pp (Bc1) 50% purple phenotypes
pp (Bc1) + pp (Bc1) = pp, pp, pp, pp (F2) 100% purple phenotypes
This combination works with the advantage of higher recessive phenotype presence throughout the process while just seeking out Purple plants on a singular basis.
point out any mistakes you see