Re: Weird Genetic mixes
Vickie:
2 genes are required for each trait or each factor effecting each trait.
Since each parent may only pass 1 of each pair; that's where you get the 50%
of genetic heredity for each parent. As to which genetic factors make up each
50% passed on: that's why I call it genetic slot machine (or crap shoot).
Chance plays a big part. By selecting for certain factors, we eventually
narrow down the odds by removing many variables, & leaving many homozygous
(both genes the same) pairs. In this way, chance is forced to make the
selection we want from it: there is only the gene we want, & it's there twice.
By back-crossing hybrids to the parent carrying the most desirable
characteristics, you are more likely to achieve your aims, but the hybrid
cross originally diffused a lot more genetic material into the genetic pool, &
it may take a couple of generations to sift through the new material to select
& concentrate the characteristics you want.
Another way to handle this may be just to breed phenotypically (select for
physically expressed characteristics). By selecting & reselecting for pumpkins
that are large & produce consistently large pumpkins, you will still be
selecting for & concentrating the traits you want. The only problem is that
each variety may not achieve size for exactly the same genetic reason. EX:
variety A is a giant, but more than half its size is due to the ability to
better utilize nutrition. Variety B is another large pumpkin, but its size is
due to its ability to grow better with less water. Now assume both
characteristics are controlled by only 1 gene pair, but both are recessive
(require both the same in the pair to be effective) Now, when you cross them,
suddenly, you have split up the "winning combinations". So here's your
dilemma: do you backcross, to try to get one of the pairs to attain a
homozygous double recessive: or do you outcross to another large pumpkin,
hoping this one will be dominant for size.
A real breeder takes the time (probably several generations) to use back
crosses (& full sib crosses) until he has developed a strain homozygous for
both recessive traits. Then He tries to cross in the other strain (dominant
size gene) so he can grow a pumpkin big enough to swallow New Jersey. (this
would take several more generations)
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