dominance and codominance...

Dear VPI,

When someone uses the term "dominant" as opposed to "codominant," what is the general difference?  For example, I read a Spider Mojave was the offspring of a Spider (dominant) X Mojave (codominant).  I'm probably missing something but it's just kind of confusing.

Thanks.   Jeff

Dear Jeff,

Dominant is a relative term--a trait (in this example, "spider") is "dominant" over another trait that is "recessive" (in this example, "normal" is recessive). The dominant trait ("spider") is expressed in both the heterozygous condition (spider x normal) as well as the homozygous condition (spider x spider). Both genotypes appear the same, in this case they both appear as "spider." There is no "super-spider."

When a trait is "codominant," then it has to be codominant with some other trait. The codominant trait (for example, "Mojave") when in a heterozygous condition with its co-trait (in this case, "normal") has a different appearance (in this case, the het appears as "Mojave") than it does in the homozygous appearance (Mojave x Mojave appears as leucistic).

Does that help any? Our book, "Ball Pythons, The History, Natural History, Care, and Breeding" has a long chapter on the genetics of snake breeding, as well as a lot of information on the morphs.  DGB