I think you where headed in the right direction the post before this one.Originally Posted by rebel750
Remember that heterozygous means having an unmatched pair of whatever genes you are talking about. Het does NOT necessarily mean normal looking or even half way to something else. Heterozygous just describes the genotype.
Individual snakes have a genotype classification for a given gene, like heterozygous for albino (having an unmatched pair, one with the albino mutation and the other copy of the same gene without the albino mutation).
Dominant is a way of classifying a specific gene mutation relative to another version of the gene (usually the normal or wild type version). It is constant for the mutation regardless of if the individual snake you are looking at is heterozygous or homozygous for that mutation.
The pastel mutation is an example of a co-dominant mutation (some would argue incomplete dominant but that's another discussion). A ball python that is heterozygous for the pastel mutation has an unmatched pair, one pastel mutant copy and one normal for pastel copy. This creates the pastel phenotype (another way of classifying an individual snake by how it looks). So all pastels are heterozygous at the pastel gene, they have an unmatched pair, a normal for pastel version from one parent and a pastel version from the other parent. The pastel mutation is still co-dominant even if you are looking at a super pastel phenotype. It's the genotype that changes from heterozygous to homozygous mutant between the pastel and the super pastel. The mutation type stays the same. In fact it the relationship between how the hets and the homozygous mutant genotypes look that defines the mutation as co-dominant. Unfortunately you sometimes read about the “dominant form” of a co-dominant mutation when really they are talking about the homozygous version and I think this causes much of the confusing misuse of “dominant”.
Pinstripe is the first proven dominant ball python mutation. The mutation type is classified as dominant because the homozygous pinstripe looks the same as the heterozygous pinstripe; both have the mutant pinstripe phenotype.
Spider is a tough one because 20 years after the founder was bought we still don't know the mutation type. If the homozygous spider genotype is lethal it could explain why we haven't seen a public proven homozygous spider yet. It could also just be that no one has been all that interested in producing and proving one. If spider is homozygous lethal I think this would technically count as co-dominant. The phenotype of the homozygous spider (dead, perhaps even before eggs are laid) would be different than the phenotype of the heterozygous spider (cool spider pattern with a tendency to wobble but alive).
So, the normals from a spider breeding are completely normal for spider. Because spider is not recessive, if a ball gets even one copy of the mutation it does not look normal. As far as we know all the spider phenotype balls produced so far are heterozygous for the spider mutation. They have one spider and one normal for spider copy at the spider locus and that's the real definition of heterozygous.
Mojaves like pastels are known heterozygous animals because they are co-dominant so the hets and the homozygous are both mutations but are different from each other.
A pinstripe hatchling from pinstripe X pinstripe would be a 33% chance homozygous pinstripe until breeding results eventually prove it het (producing some normals) or homozygous (producing a large number of only pinstripes bred to non pinstripes).
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