Reptile & Amphibian Forums

I don't see how my post could be seen as mean spirited and serving no useful purpose. If people want to selectivly breed animals, wouldn't actually knowing about genetics be helpful? For instance, all the talk about the genetics of Jaguar pythons recently. Several people made comments that indicate they have very wrong ideas about how genetics work. Several people mentioned genes being co-dom. One person went so far as to say hypomelanism in boa's involves codominant traits. This is absolutley incorrect. You cannot have co-dominant genes (actually we would be talking about alleles) coding for traits like pigment and pattern. It does not work that way. All patterns and pigments are the result of dominant vs. recessive allele expression simply, and polygenic gene expression complexly. For instance, the human eye is coded for by 14 different genes. All of them are either dominant or recessive.

By definition, codominance is a pattern of inheritance in which both alleles of a gene are EQUALLY expressed. This only happens in traits such as human blood type. Type O is recessive, and type A nd type B are both dominant. Cross type A with type B and you get type AB. Both blood type's antigens are present in the same form as they would be in Homozygous A, or B.

In the previous discussion about Jaguar carpets, someone said the offspring being 50-50 suggests codominance. That is absolutley wrong. It is also wrong to assert that a striped pattern (that may or may not be genetic) is due to codominat alleles. You could come up with a vast number of scenerios to produce the 50-50 Jags with simple dominat/recessive genes. Here is just one:

Let N = normal
Let n = Jaguar

take a het for jag and cross it with a jag

Nn X nn = Nn Nn nn nn = 2Nn:2nn, your 50/50 ratio.

If you want me to I could show you how get your degrees of hypomelanism in the boas polygenically, with only 2 dominat alleles and 2 recessive alleles. But I guess that wouldn't serve any useful purpose would it? Would it serve any useful purpose to know enough about genetics to accurately predict the inheriatnce pattern of Jaguar carpets? Guess not, that would be mean spirited.
Paul Kemes

This is a much better post than your last one. I still don't see why you got so bent out of shape with Katt, though. From the way I took it, she was only answering a question that I had asked her about a pet snake. She wasn't offering a genetic theory, and she didn't even mention breeding the snake and selling offspring.

The definition I've heard of codominance is different than yours in your post. I've always understood codominance to mean that a heterozygous animal will be halfway in between the two homozygous types, eg. with normal, pastel, and super pastel ball pythons, or with normal, tiger, and super tiger retics. If there is no super form produced when the animal is homozygous for the mutation, then it is dominant. I've also heard of this labeled as incomplete dominance--maybe this would be a better term to use. If the super examples above don't match with the true definition of codominance, then the whole herpetocultural community is using the term incorrectly.

Jake

I always thought codominance was defined as the hetero animal expressed the trait and the homo just expressed it to a greater extent. If the herp community is using the wrong term it wouldn't be the first time. It has always bothered me they use the term F1, F2, F3 to describle hypo boas also( mistakingly using it in place of first generation, second gen, third gen offspring). Those terms are used to describe something totally different(though I don't quite know what those terms are used for I'll have to dig through my horticulture textbooks). I would like to hear more on the subject of Jaguar genetics from those that are working with the project now.

Not to make an excuse but I get that way when I rush myself.

Also, I would agree that incomplete dominance would be a much more accurate term. I do belive the term co-dominant is misused. Regarding the tiger retic genes, super pastels and the like, I will explain in a seperate post the way it works (as I understand it) polygenically, with just a dominant and recessive gene leading to varying degrees of expression. The key is that far more times than not, a trait is controlled by more than one gene.

Paul Kemes

I for one am very interested to learn all I can about genetics.

We are all wound pretty tight due to the shenanagins(sp?) of the last few days. It would be nice to have a real 'Adult' descussion again...

Co-dominent is an expression that has been used for some time with python breeders. Is this an impossible occurence? What type of gene is a tiger retic? Just curious.
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http://www.moreliapythons.com

I could be a jerk can't I? I'm sorry, i'll quit with the sarcasm.
Paul

nm

Hello,
wanted to touch up on Jaguar genetics.. I read your post made sense to me.. however It only takes one male Jaguar and a WT/Normal Female to produce the 50/50 ratio. None of the proposed "hets" have been bred back to a True Jaguar, nor have the proposed "hets" been bred together
What do you think makes that work?
And the original Jaguar has produced, Jaguars, Hypo Jaguars, Red Hypo Jaguars, and the greatest, a Banana Jaguar..

Plus, the normal siblings from the "Hypo" Jaguar to unrelated female, look nothing like their mother or father, but maybe a little bit of both, the bright yellow banding from the father, and the pattern from the mother. Seems like I read somewhere that Co-Dominant hets don't look like either of the parents... I have one that is extremely nice, not yellow though, but red in the banding I will post some pics,

Many thanks for your Time!!!
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Best Regards,
Cori
www.snakeroom.net