Posted by:
Paul Hollander
at Tue Feb 28 18:21:37 2006 [ Email Message ] [ Show All Posts by Paul Hollander ]
Unfortunately, the ball python people (other than Randy Remington and a few others) don't know beans about genetics. 
I use the loose definition of codominant and incomplete dominant that I was taught when I worked at the Iowa State University Genetics Laboratory. Loosely defined, both codominant and incomplete dominant mutant genes have heterozygotes that can be reliably distinguished from both homozygotes. In other words, a snake with a codominant (or incomplete dominant) mutant gene paired with the normal version of the gene doesn't look like a normal snake (with two normal genes) and doesn't look like a snake with two copies of the mutant gene.
The only way to distinguish a codominant from an incomplete dominant mutant is to get data on the functionality of the gene products. That is practically nonexistant for snake mutants. So there is no point in making a big deal on codominant vs. incomplete dominant. And, for what it's worth, functionality of the gene products is not part of the definition of either a dominant mutant gene or a recessive mutant gene.
As for blood red, we have to separate the red color from the mutant gene that affects the pattern when we talk about the blood red morph. The red coloration is reputed to be the result of selective breeding. Cross a blood red to a normal corn, and the babies are likely to be redder than the normal but less red than the blood red. But the red coloration is of no great concern because pewters aren't red.
The pattern mutant is called "diffused", "blood red", "blood red pattern mutant", or some such. The genetics have not been fully worked out yet, as far as I know. The first mention that I saw said that it was a recessive mutant. Other people say that you can tell the difference from normal if the snake has even one copy of the blood red pattern mutant. Even if that is true, my impression is that the pattern is much less defined when there are two copies of the blood red pattern mutant than when there is only one in the gene pair. So in my opinion, a good pewter should get a copy of the blood red pattern mutant from both parents, so that it has two copies of the mutant rather than one copy paired with a normal gene.
Hope that helps.
Paul Hollander
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My best answer to blood red. (more) - Paul Hollander, Tue Feb 28 18:21:37 2006