> From: [EMAIL PROTECTED]
> Date: Thu, 5 Apr 2001 06:59:29 -0400
>
> I don't think that labeling any color trait or pattern- like jungle or
> circleback or high yellow or tangerine as a breedable trait is an accurate
> representation. Its misleading because breeding the animals cannot produce
> predictable results.
Perhaps the most honest way of labelling these animals would be e.g.
'from a high yellow line', 'from jungle parents' etc.
The problem is that most traits of interest are controlled by multiple
genes and often influenced by environmental factors as well. Some
examples would be height or skin color in humans, and milk production
in dairy cattle. This gives the appearance of 'blending inheritance'
which was the predominant model before Mendel's work was rediscovered
about 100 years ago. People observed that if a tall person and a short
person had children, the children were usually intermediate, ditto if a
dark-skinned and a light-skinned person had kids together. So what was
done for thousands of years of pre-scientific animal and plant
breeding, and is still done for most economically important characters,
is to select individuals with the most desirable traits to produce the
next generation. This concentrates desirable alleles of the genes
involved into each successive generation.
So with polygenic traits in leopard geckos, if you want to produce high
yellows, get the yellowest geckos you can find, breed them together,
and save the babies with the best color to be parents of the next
generation. If you can't breed them any yellower, cross in unrelated
animals, which may carry yellowness alleles not present in your strain
- you may lose some color in the first crosses but get back more
later. Even if polygenic traits appear to be 'blending inheritance',
the Mendelian stuff is still going on underneath, though not visible.
Pattern traits can be a bit trickier. There may be a lot of genes
involved in determining the arrangement of black markings on a gecko's
skin. 'Jungle' seems to mean a streakier or blotchier pattern instead
of mostly round spots. I don't know whether the various circle back or
striped patterns can be made to breed true. For one thing, a
particular pattern may appear only in heterozygotes. For another,
some traits may be variably expressed even in animals with the same
genotype for these traits. Also, just because we *see* a pattern,
doesn't mean that it is genetically determined. There was some work
done to select Dalmation dogs with evenly distributed, symmetric spot
patterns that turned out to be futile, since it wasn't under genetic
control. The dogs just had spots, and picking out the ones with more
aesthetically pleasing spot patterns didn't select a group with spot
genetics any different from the others. For a facetious example,
imagine that you hatch a baby leo that has your initials in black
markings on its head. This doesn't mean that you can establish an
'alphabet' strain that will all have roman letters on their heads!
(Btw, one of my hatchlings last year had a very clear CC on its tiny
skull. :-)
I could ramble on like this for longer, but won't unless asked.
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