"K Barrett" wrote
My question is: Isn't that probability kind of small? Or maybe my question
is: Is that a small probability? Is that what you meant by Helmut
overstating his point?
K Barrett

Kathy -
Not really, as all the discussion so far has been on population
genetics rather than hybridizing genetics. Granted, the population as
a whole would have small numbers of pure AD genes from the original AB
x CD cross.
*BUT* hybridizers don't cross populations. They want all the "best"
plants for future generations. So in the original scenario, if A is a
white, and D is a large flower, anyone looking to hybridize further
would search thru the F1 progeny for whites to cross with large
flowers. So a total random analysis of the population is skewed by
human intervention. By the time you get down to the F4, F5
generation, it is more than possible that all of the B chromosomes
have been bred out of the gene pool.
While this would be untrue/rare for population genetics, it is more
than possible for genetic selection by hybridizers. Especially when
we get to the F4 generation (great-great-grandchild) where a total
random selection would only result in a small fraction of B genes
anyway. (no, I won't do the math for you, LOL)
This is especially true for the genes that "express" for flower or
vigor qualities. If you are breeding for fragrance, you toss any
non-fragrant plants. Same for reds in a white breeding program, and
usually runts are gone also.
If I remember the original statement, he said that "some complex
hybrids" would have no genes from the original parent B. This is
correct, especially for breeding programs with certain goals in mind
and the further away from the original AB breeding. While there would
be many with some B genes, there would be some plants with none, if
the B genes didn't fit the breeding goals.
If you want large ferocious guard dogs, you try to breed out all the
poodle qualities, LOL!!!

jimwatts