# Co dominant genes



## Ashe (Jun 10, 2011)

Hello all
I've been reading up on about the genetics of the designer breeds of reptiles and for the best it's simple enough to understand but when I've come to the sections regarding co-dominant genes I come to the point where I look like a dribbling idiot. But I think it may have finally clicked and I'm looking for confirmation 
The best way i can break down to is that the animal in question visually represents the traits of two individual morphs the best example I can find of this is the spinner morph which contains the spyder and pinstripe genes which exist at different locus points in it's genetic make up and therefore don't conflict which each other so both characteristics can be seen in the one snake 

Does this sound right or am I filling myself full of ****

Thanks for any input


----------



## dani11983 (Mar 17, 2007)

Thats not co-dominance.

Co-dominance is when two alleles of a gene in a heterozygous animal are expressed both visually and equally. 

Alleles are different types of the same gene on the same locUS (position on the chromosome)

Simple example (it's not this black and white though!)

One gene pair decides hair colour. A person always has two genes for hair colour. 
If they are heterozygous they'll have one allele for black hair and one allele for white hair. Their phenotype is grey hair because neither is dominant to the other. 
If black was dominant then the person would have black hair and need to have two copies of the white allele to be visual white hair.

My point: The situation you describe is not true co-dominance but the interaction of two completely different genes, which I assume as they are (probably nice) morphs must be homozygous (a pair of each gene) to be apparent in the phenotype (visually).


----------



## lee anderson (Oct 13, 2009)

Ashe said:


> Hello all
> I've been reading up on about the genetics of the designer breeds of reptiles and for the best it's simple enough to understand but when I've come to the sections regarding co-dominant genes I come to the point where I look like a dribbling idiot. But I think it may have finally clicked and I'm looking for confirmation
> The best way i can break down to is that the animal in question visually represents the traits of two individual morphs the best example I can find of this is the spinner morph which contains the spyder and pinstripe genes which exist at different locus points in it's genetic make up and therefore don't conflict which each other so both characteristics can be seen in the one snake
> 
> ...


i take it were on royals and a spinner is two dominant genes to make it easy co dominants make super forms like bels,super pastels,ivories


----------



## Ssthisto (Aug 31, 2006)

dani11983 said:


> My point: The situation you describe is not true co-dominance but the interaction of two completely different genes, which I assume as they are (probably nice) morphs must be homozygous (a pair of each gene) to be apparent in the phenotype (visually).


Pinstripe is a dominant trait, so you only need one copy of the gene to produce a visual Pinstripe (and two copies doesn't look any different).

Spider *may* be a codominant trait... but not in the way one typically thinks of it. Because nobody's come out with a proven homozygous spider (despite plenty of breedings that should have produced one), it's quite possible that the homozygous "super" form of spider is "doesn't develop into a live hatchling."


----------



## paulh (Sep 19, 2007)

Ashe said:


> Hello all
> I've been reading up on about the genetics of the designer breeds of reptiles and for the best it's simple enough to understand but when I've come to the sections regarding co-dominant genes I come to the point where I look like a dribbling idiot. But I think it may have finally clicked and I'm looking for confirmation
> The best way i can break down to is that the animal in question visually represents the traits of two individual morphs the best example I can find of this is the spinner morph which contains the spyder and pinstripe genes which exist at different locus points in it's genetic make up and therefore don't conflict which each other so both characteristics can be seen in the one snake
> 
> ...


Full of ****. But that is not surprising because the authors of many of the herper web sites don't understand codominance.

First, with codominance, there is only one gene pair. A spinner has two gene pairs. One gene pair has a spider gene and a normal gene in it and the other pair has the pinstripe gene and a normal gene in it.

Pastel in royal pythons is a good example of codominance. There is one pair of genes. That pair can contain two pastel mutant genes or two normal genes or a pastel mutant gene and a normal gene.

two pastel genes --> super pastel appearance
two normal genes --> normal appearance
one pastel gene and one normal gene --> pastel appearance

You can look at a pastel royal, a super pastel royal, and a normal royal and see that they are different. A pastel royal does not look like either the normal or super pastel royal. Therefore, you can look a pastel royal and infer that it has a pastel mutant gene paired with a normal gene. No breeding test is needed to figure out the genes present.

There are many ways a creature with a codominant mutant gene paired a normal gene can be different from a creature with two copies of the normal gene and a creature with two copies of the mutant gene. It can be more or less intermediate in appearance, like a pastel royal python. It can show the action of both genes, like the AB blood type in humans. It can be superior in some way to both of the others, like sickle cell trait in humans in malarial areas. It can be inferior in some way to both of the others. Or there can be some other difference.

See also the last post in the RFUK genetics forum "Learning Genetics" sticky. It's my no frills genetics guide, which includes the difference between dominant, codominant, and recessive mutant genes.


----------



## MP reptiles (Dec 30, 2010)

paulh said:


> Full of ****. But that is not surprising because the authors of many of the herper web sites don't understand codominance.
> 
> First, with codominance, there is only one gene pair. A spinner has two gene pairs. One gene pair has a spider gene and a normal gene in it and the other pair has the pinstripe gene and a normal gene in it.
> 
> ...


 Yes what you said is correct but then you have to bring in predicted percentages so 50% of babie bred to a normal will be dominant heterozygus or a pastel with one copy of the gene and 50% of the babies i think(not sure what normal is classed as) will also be dominant heterozygus but of course you could end up gettting all pastels or in fact none at all. Im sure you know this and i hope the op understands it a bit more fully.


----------



## Ashe (Jun 10, 2011)

Back to the dribbling idiot phase for the moment


----------



## dani11983 (Mar 17, 2007)

Ssthisto said:


> Pinstripe is a dominant trait, so you only need one copy of the gene to produce a visual Pinstripe (and two copies doesn't look any different).
> 
> Spider *may* be a codominant trait... but not in the way one typically thinks of it. Because nobody's come out with a proven homozygous spider (despite plenty of breedings that should have produced one), it's quite possible that the homozygous "super" form of spider is "doesn't develop into a live hatchling."


I don't know about the specific genes in this species. I was commenting on co-dominance in general (as a biology teacher) and making an assumption about the genes in question. 

Assumption makes an ass out of me clearly!


----------



## igmillichip (Feb 7, 2010)

Ashe said:


> Back to the dribbling idiot phase for the moment


You'll only dribble like an idiot if you read dribble. 

I can't count the number of web-links that have been recommended 'as good ones' to put on our website....but when I review the said 'great link', they were mainly absolute dribble. If I were a snake-breeder and didn't know any better then I'd have probably OK's them, but I can't support sites that make out they are scientific when they aren't.

On their own, they are probably fine as a unique self-contained entity that may have no real meaning outside of the 'snake' topic......the problems come when you go to a proper scientific source on genetics.

There are some good breeder genetics sites out there.....but finding them via google is going be like finding a needle in a whatever it is.

But, it does depend on what you want to get from the info.......if it is a recipe for 'cross this with this will get this....' then that could be good info; if it is looking at trying to understand the science then that is a different topic.
Horses for course and all that.

ian


----------



## paulh (Sep 19, 2007)

MP reptiles said:


> Yes what you (paulh) said is correct but then you have to bring in predicted percentages so 50% of babie bred to a normal will be dominant heterozygus or a pastel with one copy of the gene and 50% of the babies i think(not sure what normal is classed as) will also be dominant heterozygus but of course you could end up gettting all pastels or in fact none at all. Im sure you know this and i hope the op understands it a bit more fully.


A lot of the web sites bring in predicted percentages. Which is one of the reasons for my statement that those authors do not understand codominance. 

If you mate a heterozygous creature (with a mutant gene paired with a normal gene) to a homozygous normal creature (with two normal genes), each baby has a 50% chance of being heterozygous and a 50% chance of being homozygous normal. This is true no matter whether the mutant gene is dominant, codominant, or recessive to the normal gene.

In other words, dominant, codominant, and recessive have NOTHING to do with predicted percentages. They have EVERYTHING to do with the appearance of the creature that has a mutant gene paired with a normal gene.


----------



## MP reptiles (Dec 30, 2010)

yup its completely random because fertilisation is random.


----------



## paulh (Sep 19, 2007)

dani11983 said:


> I don't know about the specific genes in this species. I was commenting on co-dominance in general (as a biology teacher) and making an assumption about the genes in question.
> 
> Assumption makes an ass out of me clearly!


But you did good up to that assumption.


----------

