Posted by:
RandyRemington
at Sat Jun 7 22:25:27 2003 [ Email Message ] [ Show All Posts by RandyRemington ]
Technically there could be a couple of exceptions to the expected in addition to the obvious of one morphs completely covering another (like if an animal was homozygous for both some sort of pure white recessive leucistic and striped I would expect leucistic to completely cover striped so it would only look like a leucistic, no color to show the stripe in).
One exception is if two mutations turn out to be alleles of the same gene. Say for example, it turns out that two different mutations of the same gene create both clown and piebald (just an example). When someone breeds a clown to a piebald there would be no normal copies of that gene so the babies would not be normal. They might come out clown looking or piebald looking or something in-between or totally different but not normal. Striped and Motley in corn snakes are believed to be alleles.
It is also possible that two mutations could be different mutation of different genes but the genes could be close together on the same chromosome. If for example this turned out to be the case with the green and granite mutations in Burmese pythons (again, just an example) you would get the expected normal looking double hets when breeding green to granite but it would be much more difficult than 1 in 16 to produce the double recessive green labyrinth. This is because each double het has one copy of the green/labyrinth chromosome with the green gene and one copy with the labyrinth gene. The only way it can create a single copy for its offspring with both mutations is for a crossover to happen in the right direction between the two genes while it is copying that chromosome. Depending on how close together the two genes are this might be very unlikely. In Syrian hamsters, long hair and banded are on the same chromosome so it took a while to create the first long haired banded hamster and if you now started out with long hair bandeds it would take a while to separate the two mutations and breed back to short hair.
On a different subject, there is also the possibility of a sex linked gene showing up some day. Say for example, it turned out there was a type of leucistic that occurred on the Z chromosome (again, just an example). In snakes, a male's sex chromosomes are ZZ and a female's are ZW. This mutation might have a different effect on females which don't have a second Z to balance it out than in males. Maybe a male would need two copies of this gene to look leucistic but a female could look leucistic with only one. A het male might even look partially leucistic. A female leucistic would produce all het sons and normal daughters, only a male leucistic could produce all hets. There are lots of other twists to sex linked genes.
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Twists - RandyRemington, Sat Jun 7 22:25:27 2003