Unlike recessive traits, co-dominant traits are expressed visibly in the heterozygous form, but also manifest themselves differently in the homozygous form. The patterns of inheritance and statistical numbers for co-dominant (or co-dom) breedings are the same as those described in the “Recessive” page, however, since the hets are all visible it is much easier to know what you are producing. It also means that you can reproduce the trait in one generation with only one parent carrying the gene.
We are going to use the pastel trait in our examples since it is a common co-dominant morph that pretty much every ball python enthusiast is familiar with. A pastel is actually an animal that is heterozygous for the pastel gene. When you breed a pastel to a normal, the statistics are actually the same as a het recessive x normal breeding. Half of the offspring (statistically) will receive the pastel gene, so the half of the resulting clutch should be normal, the other half pastel. So instead of possible hets, you get visible hets, making all the “50%” stuff unnecessary.
So what happens when you breed two pastels together? This would be a het x het breeding in essence, so just like in a recessive het x het breeding, one can expect half the clutch to be pastel, a quarter of the clutch to be normal, and a quarter of the clutch to be homozygous for the trait (commonly called a “super” form).
So let’s talk a bit about “supers” before we get into some more examples. The homozygous, or super form, is what separates co-dominant traits from dominant traits. A dominant trait (like the spider morph for instance) has no super form, meaning that it appears the same whether it is heterozygous or homozygous. But a homozygous pastel is visibly different than a heterozygous pastel. A super pastel is generally much brighter and more washed out in color, and often much busier in pattern. Some morphs super forms are even more drastically different from their het form. Lesser platinums, butters, and mojaves are all co-doms that produce blue eyed leucistics in their super form (all white with blue eyes). Fire ball pythons are black eyed leucistics in their super form, and black pastels and cinnamons produce all black or dark brown supers.
Back to our super pastel crosses. Let’s say we breed a super pastel male to a normal female. Just like when you breed an albino to a normal, producing all 100% hets, all of the offspring are going to pick up one of the pastel genes from the super pastel. Since “super pastel hets” are pastels, you get a whole clutch of pastels. Pretty nice, eh?
Let’s take our super pastel male crossed with a pastel female. Again, all of the offspring are going to get a pastel gene from the sire, making them all pastel at the very least. Half of the babies (remember- statistically!) are also going to get a pastel gene from the mom (who is technically a het for the gene), making them super pastels. So in this scenario, half the clutch should be pastel, half super pastel.
So that leaves the obvious super pastel x super pastel cross. All of the babies in a super x super cross are going to be super pastels. Just like in our albino x albino cross in the “recessive” lesson, every baby is guaranteed to get one pastel gene from the male and one from the female.
So that’s the way co-doms work. It’s just like recessives, but everything is visible. No possible hets to ponder – just normals, morphs, and super morphs. This is one reason co-doms are more affordable in general than recessives. You can buy one co-dominant male, breed him to a bunch of normal females, and the next thing you know you are up to your ears in baby ball python morphs. That’s not to say there isn’t more to be done with co-doms, however. When you start crossing co-doms together, things can get just as tricky as multiple recessives. We will get into a whole lot of that in the “Multiple Morph” page!