I have a Question. So in my research about BP genetics something confused me. What is the difference between Dominant and Co-Dominant? at first it sounded like the difference is that Co-dominant has Supers and Dominant doesn’t. But I know that’s not it because Spider has a Super form even though it is lethal.
Also both Pinstripe and Leopard also have a Super form even though it isn’t visible. So what is the difference Dominant and Co-dominant?
So what you’re getting at is actually correct, there’s just a couple of common misunderstandings in the reptile-genetics hobby in general.
Firstly, Co-dominance is usually used incorrectly to mean incomplete-dominance. Secondly, Super is also sometimes used incorrectly to just mean two copies of a trait rather than the super-form.
But the difference between a normal dominant and an incomplete dominant is that the incomplete dominant has a visibly different complete/super form, whereas dominant does not, meaning that while you can have an animal that is homozygous for that dominant, it doesn’t display differently.
So:
A dominant trait is expressed whether there’s one or two copies on the allele. They do not have a super/complete form, because the super/complete form is impossible to tell from the het-form, thus already complete.
An incomplete-dominant trait is expressed in one (incomplete) way when it is present on one allele, and a different (complete/super) way when it is present on both. They can be allelic with other incomplete dominant traits and create a third presentation.
Co-dominance: The trait is occupying an allele with another trait that is also dominant. They both show on the phenotype pretty much equally.
Co-dominance is pretty rare, Im not sure it’s even been proven in reptile phenotypes yet, but one example is blood-types in humans. If you get an A from your mom, and a B from your dad you get AB type blood, as both are dominant. If im not mistaken, tortoiseshell cats are another, where the red trait is linked to the X chromosome, so if the cat has one X with the red trait, and one X without the red trait it’ll result is a mix of both.
Ok thank you that makes a lot more since. But then shouldn’t Spider be a incomplete-dominant trait because it has a Super form?
It is an incomplete dominant:
Spider - Ball Python Traits - Morphpedia (morphmarket.com)
To add to this, incomplete dominant traits with a lethal super-form are sometimes called recessive lethals 
Ok yes Spider is a incomplete dominant. One paper explaining ball python genetics had Spider listed as a dominant gene, and so my brain remembered it as such.
Interesting. Do you know why it’s sometimes called recessive lethals? I have a vague idea of why but deferentially want input.
That’s fair, reptile genetics can be a jungle to navigate sometimes
It’s because you need two copies to express the lethality, so the lethality itself is recessive. There’s also dominant lethal, where you only need one copy for it to be lethal. They’re pretty rare as the carrier usually dies before they can reproduce, but diseases like huntington’s is considered a dominant lethal
That makes a lot of since.
and thank you for clarifying for me
Autumn mostly covered it but allow me to be explicit: Co-dominant does not (and never has) described a mode of inheritance
Co-dominance describes a relationship between two gene. I have covered this in numerous posts here and also numerous podcasts
Short version: Think of co-parenting. I have a child, ergo I am a parent. I co-parent this child with my ex. I have a second child from my second marriage. I do NOT co-parent this child with my ex. It is the relationship between my ex and I via the first child that defines the condition of co-parenting
And it is the same thing with co-dominant genetic expression. A conditional relationship between to genes/alleles.
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Part of that is likely the date of publication but a larger part is that the individual that coined the popular usage of “co-dominant” in the reptile hobby had only a junior high school-ish level understanding of genetics but was, unfortunately, highly influential as a pioneer at the beginning of the morph craze and his completely incorrect usage of terms continues to haunt us despite actual geneticists clarifying the facts
Which pioneer was this if you don’t mind me asking? Pete Kahl?
I’m a little surprised at your stance on that because from what I remember Warren Booth, a geneticist, was a proponent of the “codominant” label and made a solid case against “inc. dominant”.
Edit: It was Paul Hollander, not Warren. From what I recall Paul was a geneticist as well. He was the go-to genetics guy back when I frequented boa forums in the early 2000’s. I think you and I may have discussed this in 2019 or so as well.
Different texts have different definitions of codominant and incomplete dominant. I know of three that are more or less accepted.
The oldest definition is that in intermediate dominance, the heterozygote is more or less intermediate in appearance between the two homozygotes. For example, in many flowers the heterozygote produces pink flowers, one homozygote has red flowers, and the other homozygote has white flowers. In codominance, the heterozygote has some areas that look like one homozygote and other areas that look like the other homozygote. For example, the human A blood type, B blood type, and AB blood type.
If we use the traditional definition, we also need to add a third category–overdominance. The heterozygote’s appearance is outside the range of the two homozygotes.
Here is the most recent definition that I have seen. In incomplete dominance, one allele has a functional product and the other allele does not. This produces a blend–pink flowers instead of white or red flowers. In codominance, both alleles produce functional products. If the test is sensitive enough, both alleles can be detected. For example, in the human AB blood type, both A and B antigens occur on the surface of the same red blood cell and can be detected. In less sensitive tests, a blending can occur as in the Tonkinese cat. Both the Burmese and Siamese alleles produce melanin, but different amounts. The Tonkinese cat has one of each allele and produces an amount of melanin roughly intermediate between that of the Burmese and Siamese cats.
The third definition basically says that nobody has figured out whether only one or both alleles have a functional product. Until that is figured out, call the two alleles codominant to each other, because “codominant” requires fewer keystrokes to type than “incomplete dominant”. And define codominance as each of the three possible genotypes producing its own characteristic appearance.
IMO, a five part classification scheme (dominant, recessive, incomplete dominant, codominant, overdominant) is too inconvenient for newbies and most breeders.
Does the pastel situation parallel the Burmese cat or the pink flower? I don’t know, and I don’t think that anyone knows. So the second definition cannot be used with accuracy. And do breeders care about the number of functional gene products? I’ve bred a lot of birds, and the main thing I wanted to know was the identity of the bird’s genes.
That leaves the third definition. There was a paper in Bioscience magazine in 1995 (Three neglected advances in classical genetics) where the author stated he had used that definition successfully in introductory genetics courses.
“There are no codominant traits in ball pythons.”
Pastel + mojave makes pastave where the two colors blend together.
If they were codominant there would be parts of the snake looking like a pastel and parts looking like a mojave.The pastel and mojave genes are not members of the same gene complex. A pastave has two gene pairs of interest–a pastel gene paired with the corresponding normal gene and a mojave gene paired with its corresponding normal gene. Only genes of the same gene complex can be codominant/incomplete dominant. So pastave does not count.
Codominance = Parts of the snake having one appearance and parts of the snake having a different appearance. This definition is inaccurate.
The Burmese cat (cbcb) and the Siamese cat (cscs) have different colors because the cb and cs genes produce different amounts of melanin. Pictures of Burmese, Siamese and Tonkinese cats can be found in Wikipedia. The Tonkinese cat (cbcs) is intermediate in color because each color cell has a cb and a cs gene and each gene does its own thing. The two genes are codominant instead of incomplete dominant to each other because each gene produces a functional gene product.
The only snake genes that I would call incomplete dominants in the strict sense are the amelanistic and hypo genes in the corn snake. Until other genes are characterized, we don’t know for sure which are codominants and which are incomplete dominants. And arguing about which term to use is pointless.
Well I would prefer not to say who it was who rote the paper that I was reading to prevent hurt feelings. But I would say from what I know about the person who rote it, it’s at lest 2-3 yeas old.
My personal problem with calling everything inc-dom co-dom, is that like t_h_wyman said, co-dominance describes the relationship between two variants of an allele, whereas recessive, dominant, and incomplete dominant describes the relation to itself as well. Colorpoint, for example, is actually recessive on its own. Also, not all incomplete dominant genes are gonna be paired with an allelic trait. Some don’t even have any. Take Lilly White and Pinky in crested geckos. Those have clear super-forms that are distinct from their het-forms, but they’re not allelic with any other known trait. So calling them co-doms wouldn’t make sense, as they’re not appearing with any other traits. You could argue that incomplete-dominant traits are co-dom when they’re paired with other traits in a complex. But on their own they still act like a recessive, inc-dom, or dom, so it makes more sense to describe them as such, based on whether you need one or two copies, and whether it has both a hetereozygous and homozygous expression.
I was going to say, Warren has been ‘Team Inc-Dom’ for as long as I have known him LOL
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I remember Paul. He and I used to trade rounds frequently on BP back when I frequented there
To the best of my recollection, which is pushing about a decade now, Paul was not an actual geneticist but was just a biologist. He had some upper-level genetics classes as part of that degree, but he did not have the same depth that guys like Warren and Morrill and Juglander and myself received. He was also from a earlier generation of scientist (which is not a denigration, simply an observation that the base of knowledge from which he learned from was less complete from the base Warren and Morrill and Juglander and myself were learning from)
His breakdown in that thread that you quote is completely incorrect, there is really no other way to put it. I do not really have the motive force at the moment to get into they whys of all of it but I will use the most relevant - the blood types
For the purposes of the morphs we deal with (because that is all we care about in terms of the morph-driven nature of this hobby), there are only two modes of genetic inheritance: recessive and dominant
With genes that are inherited in a recessive manner, you will not see an different phenotype from the wild-type condition if only one copy of the mutant allele is present
With genes that are inherited in a dominant manner, you will see an different phenotype if one copy of the mutant allele is present
With blood types, you have three alleles: o, A, and B. We consider type-o to be the “wild-type” and it is recessive to both A and B. The A allele is inherited in a dominant manner - if I inherit just a single copy of the A allele, by phenotype is altered from the wild-type. Likewise, the B allele is inherited in a dominant manner - if I inherit just a single copy of the B allele, by phenotype is altered from the wild-type
What is too frequently overlooked in this case (and also horribly glossed over in most primary education bio classes) is that you are looking at THREE alleles. People only look at A and B and completely forget that o is a part of all of this and that the inheritance pattern is based off of the observed (or not) change in relation to the wild-type condition
So… If someone has a blood type of AB, does the inheritance pattern of those alleles differ in any way from the inheritance pattern for those same alleles if they were in someone who was just type A or just type B?
The answer is no, the way they inherit the genes is the same
The “co-dominant” label given to individuals with type AB blood has nothing to do with how the individual alleles are inherited versus the wild-type. Co-dominant instead refers to the phenotypic expression we see in situations where those two mutant alleles are behaving in the presence of the other. And and be are bot expressing in a genetically dominant manner, but neither is dominant over the other so their behaviour when, and only when, in combination with one another, is described as co-dominant
Going back to my previous, this is the same reason that I am always a parent but I am only a co-parent when it comes to the behaviour between my ex and I vis-a-vis our child
And while I do not know if you have a child, for the sake of argument let us say that you do. That then would also make you a parent. However, just because you are a parent and I am a parent, that does not mean that you and I are co-parents. Because you and I have not parenting relationship that we share
Excellent explanation Travis, makes sense completely. Thanks for taking the time to write up that response. Going back for so many years with a certain understanding it can be tough to break away from how I was taught from individuals with better scientific qualifications than I (none, lol). I appreciate that there are geneticists like yourself and Warren that have set the record straight and encouraged everyone in the hobby to use the correct terms going forward. I’m glad we have people like you around these days to point us in the right direction.