Ball python single gene morph descriptions -need feedback

[paulh]

The exact difference is clear, though. Phenotypically, there are no known co-dominant mutations in ball pythons.

As an example, when you cross a Pastel with a Spider you get a Bumblebee, which is a blend of the two mutations. This indicates phenotypical incomplete dominance. You do not get a "zebra-patterned" animal which shows areas of both individual Pastel and individual Spider pattern. That result would indicate phenotypical co-dominance. The same phenotypical blending of mutations holds true with every known mutation in ball pythons. If your professor cannot see this difference, I would be questioning their understanding of the two terms.

Bumblebee is not an example of either codominance or incomplete dominance. Two genes must be able to form a gene pair to be either. Spider and pastel are independent genes, as shown by breeding data. Bumblebee x normal produces normal, spider, pastel and bumblebee babies. If spider and pastel genes could form a gene pair, then a bumblebee x normal mating would only produce spiders and pastels.

As far as I can tell, here are the presently preferred definitions of codominant and incomplete dominant:

Codominant = the heterozygote is different from the two homozygotes because both genes contribute to the heterozygote's phenotype. Both genes produce functional products. The heterozygote's phenotype may be more or less intermediate between the phenotypes of the homozygotes, may be outside the range of the phenotypes of the homozygotes, or may show both homozygotes' phenotypes. The burmese and siamese genes in cats are codominants. Both genes produce functional products, and the heterozygote is the the tonkinese cat, which is roughly intermediate in color between burmese and siamese cats.

Incomplete dominant = the heterozygote is different from the two homozygotes. Only one gene produces a functional product, which produces the heterozygote's phenotype. The heterozygote's phenotype is generally more or less intermediate between the phenotypes of the homozygotes.

Most mutant genes have not been characterized as to whether or not they produce functional products. Some people use "codominant" as a collective term for such genes where the heterozygote is different from the two homozygotes. (The BioScience paper referenced two posts up is on the web at http://www.ringneckdove.com/Wilmer's...bioscience.htm). Others use "partial dominant" as the collective term. The pro geneticists do not seem to have settled on a collective term.

I think a case could be made that the mojave gene is codominant in the strict sense to the corresponding normal gene. Mojave ball pythons can be distinguished from both normals and super (homozygous) mojaves, and super mojaves are not pure white. The lesser gene can form a gene pair with the mojave gene, and the super lesser is pure white. If the lesser gene is nonfunctional, then it seems to me that the mojave gene's product is somewhat functional. The Russo gene is also in that set alleles; it may also be codominant to the normal gene.