Genetics....

[paulh]

So have been doing a lot of reading and studying on genetics due to the Dom, Co-Dom, Recessive terms thrown around with the occasional Allele and Locus thrown in there.. So in trying to further my understanding of what I am seeing in breeding I am starting to believe there are some truths misrepresented. The first one would be our labeling of dominant genes. Dominant gene would mean that anything on the same locus and the corresponding allele would be overridden by the dominant gene. We have called Spider and Pinstripe dominant genes, when in reality they may be dominant to some alleles but they are in fact incomplete dominant, hence the spinner that comes from the mixing of the two. Also, Co-Dominance means that there will be evidence of the individual alleles present in the resulted phenotype, for example if Mojave and Cinnamon were true Co-Dom you would see part Mojave and part cinnamon on the same snake (which from study sounds a lot like paradox but I am not even going there), instead we once again see incomplete dominance because the result in most of our breeding shows a mixing of different alleles that are not distinctive of the originals. I am not saying I have this 100% down, because I surely don't but I think based on what I read you could refer to Mojave as an incomplete dominant gene with most other allelic combinations and co-dom is mostly in reference to genes like Spider/pinstripe, but in truth these alleles lie on different parts of the genes or possibly another place on the DNA strand all together... and fire away and bash me!!! lol

You are correct in writing that herpers misrepresent some truths. That is why I prefer standard genetics definitions to the herper versions. You might like to look at the Genetics Home Reference -- http://ghr.nlm.nih.gov/handbook. It's free.

The dominant/codominant/recessive classification results from a comparison. For example, both the mojave gene and the lesser gene are codominant (for this discussion a synonym of incomplete dominant) to the corresponding normal gene. However, the lesser gene is dominant to the mojave gene. Because both the super lesser and the het lesser/mojave snakes are blue-eyed white, while the super mojave is nearly a blue-eyed white but has some pigment on the top of the head and neck. The classification is different because the comparison is to different gene. I could point to several examples (not in snakes, yet) where one gene is dominant to a second gene, codominant to a third, and recessive to a fourth.

The comparison can be either explicit or implied. "The lesser gene is dominant to the mojave gene" is an explicit comparison. "The lesser gene is a codominant mutant gene" is an implied comparison. And when the comparison is implied, the assumption is always that the comparison is with the corresponding normal gene.

[se7en]

All I know is that cinnamon + mojave looks great.






http://www.worldofballpythons.com/morphs/savannah-ball/

[Family Jewels]

Why would scaleless head/scaleless not fall under this definition?

Scaleless heads are one of the better arguments I've seen for true codominance in ball pythons. I say this because unlike most mutations, the heterozygote has parts of both phenotypes (normal and scaleless) represented in *patches*. The only problem I see with it is that it's not even close to an even distribution between the two phenotypes.

In chicken color, codominance is evenly distributed: http://www.angelfire.com/super2/bioc...Notes/wpeB.gif

In shorthorn cattle, roughly 50/50 distribution: http://www.google.com/imgres?imgurl=...CEEQMyg5MDk4ZA

In Camellia flowers, again 50/50 (-ish): http://upload.wikimedia.org/wikipedi...ododendron.jpg

etc. One (co)dominant allele is just as likely to be phenotypically represented as the other (co)dominant allele at any random point on the animal.

However in the scaleless head, the scaleless phenotype is limited to less than 1% of the snake's body and it's always in the same place... the normal allele seems pretty dominant over the scaleless allele. It sort of reminds me of het pied markers (ringers) peaking through despite their recessiveness to the normal allele. Meanwhile, in the codominant ABO blood system, a person with AB blood doesn't have 99% A antigens and 1% B antigens... the antigens are evenly distributed approximately 50/50 across the surface of the cell.

Another thing I noticed about widely agreed upon examples of codominance is that they usually involve at least three alleles at the same locus. For example, spotted and dotted lentils are considered codominant (when combined they create an equally spotted and dotted lentil), and each is individually dominant to the recessive clear allele. Likewise, A antigens and B antigens are codominant to each other, and each is individually dominant to the recessive O allele. But that's just a random tangent.

Like I said, scaleless heads make a reasonable argument for codominance... although they don't fit the picture with what we'd (ideally) expect to see, and I'll admit I don't really consider them to be in quite the same category as color and pattern morphs.



Ideally, a codominant ball python morph would look something like an extreme paradox.

[TessadasExotics]

You are correct in writing that herpers misrepresent some truths. That is why I prefer standard genetics definitions to the herper versions. You might like to look at the Genetics Home Reference -- http://ghr.nlm.nih.gov/handbook. It's free.

The dominant/codominant/recessive classification results from a comparison. For example, both the mojave gene and the lesser gene are codominant (for this discussion a synonym of incomplete dominant) to the corresponding normal gene. However, the lesser gene is dominant to the mojave gene. Because both the super lesser and the het lesser/mojave snakes are blue-eyed white, while the super mojave is nearly a blue-eyed white but has some pigment on the top of the head and neck. The classification is different because the comparison is to different gene. I could point to several examples (not in snakes, yet) where one gene is dominant to a second gene, codominant to a third, and recessive to a fourth.

The comparison can be either explicit or implied. "The lesser gene is dominant to the mojave gene" is an explicit comparison. "The lesser gene is a codominant mutant gene" is an implied comparison. And when the comparison is implied, the assumption is always that the comparison is with the corresponding normal gene.

Lesser is NOT "dominant" to the Mojave gene in any way shape or form. They are actually both codominant genes. And there is no het lesser/mojave.

[OhhWatALoser]

Lesser is NOT "dominant" to the Mojave gene in any way shape or form. They are actually both codominant genes. And there is no het lesser/mojave.

Dominant mean looking the same in heterozygous and homozygous form. Super lesser and lesser/mojave can be argued to look the same. however with the amount of yellowed out lesser/mojave I have seen i will disagree.

However every lesser is a het and every mojave is a het. Paul is using real genetic terms for the most part

[paulh]

I should have clarified what I meant by "het lesser/mojave". That is a ball python that has a gene pair made up of one lesser gene and one mojave gene. It is a visual het, not a normal-looking het.

Both the lesser gene and the mojave gene are codominant to the NORMAL gene. Comparing the lesser with the mojave gene is a whole new ball game. The relationships with the normal gene are irrelevant because the normal gene is not included in the new comparison.

A ball python with two lesser genes is blue-eyed leucistic.
A ball python with a lesser gene paired with a mojave gene is also blue-eyed leucistic. It looks like a ball python with two lesser genes.
A ball python with two mojave genes is nearly leucistic but has some pigment on the top of the head and neck.

That matches the definitions of a dominant and a recessive gene. The lesser gene is dominant to the mojave gene, and the and the mojave gene is recessive to the lesser gene.

The pinstripe gene is dominant to the normal gene because a snake with a pinstripe gene paired with a normal gene looks like a snake with two pinstripe genes. See the parallel?

[Family Jewels]

Lesser is NOT "dominant" to the Mojave gene in any way shape or form. They are actually both codominant genes. And there is no het lesser/mojave.

Mojave is incomplete dominant because the heterozygous form is a completely different phenotype from the homozygous ("super") mutant allele, and it is different from the homozygous normal allele. Same goes for lessers.

Also, all lessers and mojaves are both hets, but calling them hets is redundant since "het mojave" means "mojave", and "het lesser" means lesser. The term het does not mean hidden, it simply means heterozygous (homozygous refers to either the super or the normal animal). You are however very correct that they are not dominant to each other.

[Daigga]

I should have clarified what I meant by "het lesser/mojave". That is a ball python that has a gene pair made up of one lesser gene and one mojave gene. It is a visual het, not a normal-looking het.

Both the lesser gene and the mojave gene are codominant to the NORMAL gene. Comparing the lesser with the mojave gene is a whole new ball game. The relationships with the normal gene are irrelevant because the normal gene is not included in the new comparison.

A ball python with two lesser genes is blue-eyed leucistic.
A ball python with a lesser gene paired with a mojave gene is also blue-eyed leucistic. It looks like a ball python with two lesser genes.
A ball python with two mojave genes is nearly leucistic but has some pigment on the top of the head and neck.

That matches the definitions of a dominant and a recessive gene. The lesser gene is dominant to the mojave gene, and the and the mojave gene is recessive to the lesser gene.

The pinstripe gene is dominant to the normal gene because a snake with a pinstripe gene paired with a normal gene looks like a snake with two pinstripe genes. See the parallel?

This is not exactly true. We classify ball python morphs by their genetic dominance, not their visual dominance. while you could say that visually one gene is recessive to another, we will have a very long and non productive discussion if you mean to classify every ball python gene in relation to any other gene.

[Family Jewels]

cont'd

Also, paulh makes a good point about Lessers and Mojaves. Lesser and Mojave appear to exist at the same locus, and if they do, they must have a dominance relationship to one another (dominance relationship doesn't necessarily mean dominant, it just means that their status can be described by their relation to one or more alleles at that locus, in addition to the obvious wild type). You could argue (using paulh's logic about super mojaves looking different) that:

L is dominant to M, and both L and M are incomplete dominant to the normal allele.

Simple dominance:
LL- solid white lucy
LM- solid white lucy
MM- grey head lucy

Incomplete dominance:
LL - solid white lucy
Ln - lesser
nn - normal

Incomplete dominance:
MM - grey head lucy
Mn - mojave
nn - normal

Again, this only works because mojave and lesser probably exist at the same allele. The same can not be said about the overwhelming majority of morphs.

[paulh]

This is not exactly true. We classify ball python morphs by their genetic dominance, not their visual dominance. while you could say that visually one gene is recessive to another, we will have a very long and non productive discussion if you mean to classify every ball python gene in relation to any other gene.

I have no intention of trying to classify every ball python gene in relation to just any other gene. Only the genes that can form gene pairs. The spider and pinstripe (to name only two) cannot form a gene pair and therefore have no dominance relationship.

Family Jewels hit the bullseye when writing (above) "Lesser and Mojave appear to exist at the same locus, and if they do, they must have a dominance relationship to one another ."