So scaleless, a true Co-Dom morph?

[PhoenixGate]

Dominant mutant genes are scarce in reptiles. They are more common in mammals and birds. For example, in pigeons, a bird with two spread genes is solid black. A bird with a spread gene paired with a normal gene is also solid black. A bird with two normal genes is shades of slate gray with two black bars on each wing.

I have bred a bird with two spread genes to a bird with two normal genes. All the babies had a spread gene paired with a normal gene and were hets. All were solid black.

By the way, how are you defining dominant and incomplete dominant? When a creature with two copies of a codominant (AKA incomplete dominant) mutant gene is mated to one with two copies of the normal gene, all the babies are hets, too.

Okay, so I've seen some confusion from a few other posters on the difference between dominance and incomplete dominance. I'll add my two cents and see if it clarifies things for anyone.

A dominant gene overrides the other gene on the same locus. Just to review, a locus is the specific spot on the chromosome where a particular gene resides. A good example of dominance in ball pythons is the spider gene. There is, as far as we know, no super form of the spider gene. This means that it overrides the normal colour and pattern gene the snake carries. This also means you can't visually tell if a ball has two spider genes; since the gene is dominant a second copy of that gene won't affect what the snake looks like. The only way to know if you had a homozygous spider is if you bred that spider to a normal ball python and all of its babies were spiders.

An incomplete dominant gene means that it is expressed equally with the other gene on its loci. Any of the genes in the BEL complex are a good example of this. For example, one copy of the lesser or butter gene shows a snake that is visually different from a normal, and you can tell visually that it only has one copy of this gene. Two copies of the butter or lesser gene produces a white snake, which means that both genes on the same locus are being expressed equally, neither one is overriding the other. If the lesser or butter gene was only a dominant gene, two copies of that gene would not produce a white snake.

I've looked through several genetics books. There may be as many as 4 intermediate categories of inheritance or as few as one. I'm defining an intermediate category of inheritance in which the heterozygous phenotype can be distinguished from both homozygous phenotypes.

Here's a source that has only one category:
ghr.nlm.nih.gov/handbook/inheritance/inheritancepatterns

"In codominant inheritance, two different versions (alleles) of a gene can be expressed, and each version makes a slightly different protein (illustration). Both alleles influence the genetic trait or determine the characteristics of the genetic condition."

How reliable is the missing scale on the head as a mark of the heterozygote? If more than 5% of the heterozygotes have full scalation, then I would call scaleless a recessive mutant gene. The missing scale character would simply be a het marker.

A het scaleless bhb line or scaleless head ball python should have a few obviously missing scales, period. Until we see more het scaleless ball pythons produced from this line, we won't know if its merely confined to the head or if it has a variable range, producing anything from a snake that has only a few missing scales on its head or a 50% scaleless ball python.