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There seems to be a huge amount of confusion over what dominant, recessive, and co-dominant mean. Hopefully, I can be of some assistance, keeping this discussion as basic as possible.

DOMINANCE (complete):

A dominant gene will mask any subordinate gene. The nature of a dominant gene dicatates that regardless of whether or not the animal has one or two copies of the gene, it will look the same. "Normal" or "wild-type" colorations could be considered dominant in ball pythons...it masks any single copies of recessive genes.

Using the popular flower analogy often used to explain this concept, if you had red flowers (dominant) and white flowers (recessive), if a plant had even just one, than the flowers would all be red...but they would be just as red if two copies (homozygosity) existed.

RECESSIVE:

Recessive genes are subordinate to dominant genes. Homozygosity must exist for the gene to be expressed. In the flower example, there must be no red genes, only white, for white flowers to show.

CO-DOMINANT:

Here's where it starts to get confusing. As implied by the name, Co-dominant expressions exist when both genes affect the phenotype at the same time. In the flower, there would be both white and red flowers. In the scheme of codominance, you have three types of expression...the white flower, the red flower, and the one with mixed petals. I do not know of any snakes that can be labeled as co-dominant....they are really something different, which works in a similiar manner:

INCOMPLETE DOMINANCE:

Incomplete dominance exists when there is a sort of "blending" of the two genes. In the flower example, instead of white or red or both, you woud get pink...essentially a new phenotype completely different from the homozygous versions of the parents..red, white, and pink. Although not as obvious, our snake examples, such as pastel are the same deal....we have normal...pastel...and super pastel. Three distinct phenotypes...it just so happens that the pastel genes exhibits an incomplete dominance over the normal gene. IF pastel were truly codominant than pastels would exhibit charachteristics of both normals and super pastels at the same time. They do not. Instead, we have more of an even blending, therefore the pastel gene is incompletely dominant.

All this can get very much more involved when we take into account things like multiple alleles, epistasis, penetrance, etc, but I hope this helps to clear up the confusion between dominant and the mislabeled co-dominant traits in the ball python world.

Nice clear concise description. I like you. Thought like this will lead to a clean up of the industry. (let's work on making it an industry, what do you say?)

Dave

Ok, so technically we should be using "incompletely dominant" to describe the mutations we are currently describing as "co-dominant", right?

I guess a true co-dominant might look something like a paradox albino, but with some spots/parts completely albino and some completely normal (I don't think the paradox albino is really like this, the dark spots aren't normal either and they may well be homozygous albino but I'm just trying to think of a snake that has two different types on it's body).

It also looks like you are suggesting using "Dominant" for only confirmed “completely dominant” (my term) mutations rather than it is now being used in the trade as a sort of super category to cover a mutation for which we don't yet know if it's "completely dominant" or co-dominant (err, make that INCOMPLETLY DOMINANT, it's going to be hard to change).

Is there a term to cover a generic dominant of type not yet known? Maybe not if we are going to go by textbook terminology. It's a classic case where a scientist would not try to describe a mutation’s inheritance until the breedings had been done to test it and be reasonably sure of being correct. However, in the real world, we need a way to refer to a mutation such as the new Banana for the next few years and it gets a little wordy to say that it's "either dominant or incompletely dominant, not yet known which".

Randy,

You've got the idea. Banana has proven to be dominant, so to call it dominant would be correct. Only if it proves to have a different phenotype in the homozygous form could the gene be considered to exert incomplete dominance. To call it codominant would be stretching it, though (I don't see ANYTHING about a banana ball that resembles a normal).

The real problem with incomplete dominance is that the effect may be small, but still there...especially confusing in "gradable" morphs like pastel...a super pastel of a low grade type might not look as nice as a grade A regular old pastel (the het kind) from a nice line.

Take hypo boas for example...the super forms are not always so recognizable (hence the term possible super salmon, etc.) The only way to prove that it was super indeed is if it produces all hypos when bred to a normal. The tendency now would be to call hypo a dominant trait, but that doesn't seem quite correct because there does seem to be a difference between the het and homo versions, it's just not huge. The problem lies with the hypo gene being so variable in itself...some het forms may be so nice that they could be mistaken for homos.

Anyhow, the best example of clear cut incomplete dominance in snakes I can think of right now is the tiger retic. The het (tiger) is always discernable from the homo (super tiger)form...no mistaking it.

There are other things at work that make it confusing, but I think it's worth the effort to be as correct as possible. If nothing else it will give us more credit (image is everything) with the "outsiders" which could eventually mean something, particularly in the legislative corner.

All that sounds good and I think it is quite a bit more clear to me than it was. Here's a question.

You said banana proved to be dominant. Normals are dominant too.
If you breed banana x normal do you get some bananas and some normals? I guess I am just asking for the hierarchy of dominance. I would assume that normal is always at the top of the list of dominance (that's why there are so many of them, tee hee). If that is true than isn't a banana recessive compared to a normal? I guess that's where my confusion starts to come in. Did I just completely misunderstand something? Am I making this more difficult than it is?

Are dominant and recessive labels placed in context or are they constants?

From the clutch Will produced this year (7 eggs) three were Bananas. Whenever the Banana gene is present, it will mask the normal gene (therefore it is dominant over normal). Dominance is a "more or less" of type of thing.

In this case, Banana is more dominant than normal and normal (obviously) is more dominant that the single gene(recessive in this case) the other parent passed along (clown).

Because the other four snakes did not get a Banana gene, they look normal. In very simple terms, normal is completely dominant over the one clown gene they recieved. Hope I didn't just confuse you more. LOL!

LOL, almost! Okay I think I see where you went with that. Thanks, hehe!

Dominant and recessive are comparative terms. A is dominant to B, and B is recessive to A. So one mutant can be dominant to its normal allele (which is recessive to the dominant mutant). Or a differnt mutant can be recessive to its normal allele (and the normal allele is dominant to the mutant allele).

As more mutants turn up, dominance relationships get very confusing. Enter the wild type concept, which (among other things) says that the wild type or normal allele is the standard.of comparison. A mutant is either dominant or recessive COMPARED TO THE WILD TYPE ALLELE.

In the ringneck dove, blond is recessive to normal and dominant to white, while white is recessive to both normal and blond. Using the definition above, both blond and white are classed as recessive mutants.

BTW, the definitions for dominant, recessive, and codominant that I learned in genetics class are as follows:

Dominant mutant -- A mutant gene that produces the same abnormal phenotype in both the heterozygote (one mutant and one normal gene) and homozygote (two mutant genes).

Recessive mutant -- A mutant gene that produces the abnormal phenotype only when homozygous. The heterozygote (one mutant and one normal gene) looks normal.

Codominant mutant -- A mutant gene that produces a heterozygous phenotype that can be reliably distinguished from both the normal phenotype and the homozygous mutant phenotype. (Incomplete dominant mutants also fit this definition).

Here's the best definition that I know of for distinguishing an incomplete dominant mutant from a codominant mutant.

Codominant -- Both alleles in the heterozygote produce a functional enzyme, and the effect of the blend of functional enzymes distinguish the heterozygote from the two homozygotes.

Incomplete dominant -- Only one of the alleles in the heterozygote produces a functional enzyme, and that enzyme's effect on the phenotype is dependent on the amount produced. IOW, the effect of the blend of the functional and nonfunctional enzymes distinguish the heterozygote from the two homozygotes.

Is tiger in the retic an imcomplete dominant or a codominant? I'll tell you when somebody tells me whether both tiger and its normal allele produce functional enzymes or one of them is nonfunctional. Til then, it's an open question.

It's worth noting that the definitions for dominant and recessive say nothing about enzyme functionality, just inheritance pattern. It is useful to have a single word for the inheritance pattern that fits neither the dominant nor the recessive mode. That's been "codominant".

Enzymes are produced within cells, and the effects begin on a cellular level. Saying that an animal has one area of the body where only the effects of one allele occurs and another area where only the effects of the other allele occurs is not kosher. Because the blend of enzymes is in every cell in the body.

Piebald in the ball python would fit that whole body definition, except that the inheritance pattern shows that the mutant is recessive. 8-)

And lastly, striped in the California king snake has a variety of phenotypes in the heterozygotes, but there is no gap between heterozygote and homozygote, AFAIK. IMHO, the best category for such mutants is dominant, though "with variable expressivity" can be added if desired. And my old boss at the genetics lab used "some sort of dominant" when he didn't know whether a mutant was a dominant and a codominant.

Paul Hollander

My, I guess when I start my biology degree next spring maybe I'll use you guys as study buddies (going to try for marine biology masters to work at the new Georgia Aquarium *fingers crossed*). Quite seriously, it seems you need a degree to truly understand what the hell is going on with snake genetics these days. There is so much confusion... both in terminology and questionable record keeping. Hopefully it'll all get figured out one of these days.

I really appreciate your reply. It helped me with planning my future snake pairings and also with my current leopard gecko projects. I definitely think it will help me translate some posts and make better choices when puchasing (if a reptile show would hurry up and come back to Atlanta...grrrr).

So, do you know if anybody has actually made a chart showing dominance relationships in ball pythons? I think an excel spreadsheet is in order!

Paul is right on, and alluding to the source of the confusion...there simply isn't enough solid research done with reptiles to say for certain, and I have a feeling it will be a few years. : ) Even, then we are barely scratching the surface, considering we are talking about specific alleles when thousands upon thousands are in play (which is one of the reasons for the variance we see).

I have never seen such a chart, but that's probably because a) most people don't take it that far, although it would be useful b) most of the possiblilties have not been tried yet. Ball python breeding is still in it's infancy. So far, we've gotten expected results when double morphs have been created...but what what will happen when we get to crossing genetic stripes and spiders? Just don't know, and there are tons of crosses that have not been done and more morphs continue to pop up. Although this deals with recessive genes, a burmese python that is homozygous for patternless (green) and labyrinth will look like a patternless, but will throw labyrinth offspring when bred to another burm carrying the laby gene...completely masked. And then there is the issue of "crazy patterns" on burms that are het for traits...we've all seen it, nobody can yet explain....something's leeking trough...food for thought.

I think it would be a great idea though, and then instead of wasting time of things somebody else has already tried then people can start trying new combinations.

*Monica thinks she is talking herself into making this spreadsheet*

Here's the ultimate question though. Are the big guys in da bidness going to share info with me so I can make this thing?

Ah, hah!

I've been asking periodically for years to find out what happened to the green/labyrinth project since I first saw the double hets maybe 10 years ago. At first everyone THOUGHT green would mask labyrinth, then someone MAYBE knew someone who might have one, and now it sounds like you have good information about breedings actually proving it is so. I was suspicious that the genes for those two mutations might be closely linked on the same chromosome but it sounds like it's just masking, right?

Also, are you talking about the sporadic het sign/homozygous relationship with puzzle/granite and leopard/green? That's pretty well accepted (if not explained) now, right? I've been out of burms too long to keep up on all this stuff but I think there are some lessons that might transfer to balls.

Also, I like Paul's boss' "some sort of dominant" for the undetermined new mutations. Even following this thread I don't think we have been consistent with the use of just plain "Dominant".

I've never actually owned one, so it's heresay, I guess. The man to ask would be Bob Clark, I guess. I'll try to find out positively and post the results...I'd really hate to have posted something unfounded!

I agree...nothing would be more correct than "some sort of dominance"!