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I did a search already but couldn't find the answer. Can anyone explain the difference between a dominant and co-dominant gene? Thanx

Nat

First off, there's a slight distinction that's usually glossed over because most cornsnake genes are straight recessives...

When the term 'recessive', 'dominant', and 'codominant' are used, they don't really describe a single gene. They describe the relationship of one gene on the same locus to another gene that resides on that locus. Since most cornsnake genes do not share a locus with more than one other gene, the statement 'It's a recessive gene with respect to the wild-type gene at the same locus' has been shortened to 'It's a recessive gene'.

This distinction is important, because you can have a gene that's co-dominant with another gene and yet recessive to a third. Such is the case with ultra.

So what does it mean if a gene is recessive, co-dominant, or dominant with respect to another gene?

Most people know about recessive relationships. Amel is recessive with respect to the wild-type. Ultra appears recessive with respect to the wild-type. Neither gene will show up if it is paired with a wild-type gene at the same locus.

A gene that is dominant to another gene will always override the other gene if both genes are present at the same locus. The wild-type gene at the amel locus is dominant with respect to amel and dominant with respect to Ultra.

A gene that is co-dominant with respect to another gene will show partial expression when paired with that other gene at the same locus. Amel is co-dominant with respect to Ultra. Ultra is co-dominant with respect to Amel. Cornsnakes het for amel and het for ultra show an appearance that's partway between amel and ultra.

So... if W is the wild-type (aka the normal version) gene for the amel locus, A is the amel gene, and U the ultra gene...

W is dominant to A, U
A, U are recessive to W
A, U are codominant to eachother.

AW = Normal, het amel
AU = Het amel, het ultra (Ultramel)
AA = Amel
UW = Normal, het ultra
UU = Ultra
WW = Normal

If you think about it, the AW and UW combinations are also het for the wild-type gene... but because the wild-type gene is dominant, we don't usually think about it that way. Because alot of normals are actually only 'het wild-type' on the amel locus, it's very common for someone breeding a pair of normals to get a few amels as a surprise. Cornsnakes homozygous for wild-type on the amel locus (the WW mentioned above) are far less common than you'd think, especially in captivity.

-Kat
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"You keep WHAT in your freezer?"
"Mice. And rats. If that bothers you, I can call them 'cows' instead."

Kat you are the best! I'm amazed how much I've learned from your post. How can I ever thank you?
But please let me ask a question just as a test to see if I understand it.
If you had a single snake that was AU=ultramel on one locus and MM=motley on another locus would you have a ultamel motley?

OR, if you had a single snake that was AU=ultramel on one locus and HH=hypo on another locus and CC=charcoal on yet a third locus would you have a ultamel phantom (ultamel charcoal ghost.)

I think I get it. Are my examples correct?
If I'm right then AU on one locus and MW on another locus would be a ultramel het for motley. Is this right?

Nat

Yup. Looks right to me. That having been said the "official" notation for this sort of thing uses superscripts and subscripts, but those are a pain to type. As long as YOU know what the letters mean, it doesn't matter as much.

-Kat
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"You keep WHAT in your freezer?"
"Mice. And rats. If that bothers you, I can call them 'cows' instead."

""A gene that is co-dominant with respect to another gene will show partial expression when paired with that other gene at the same locus. Amel is co-dominant with respect to Ultra. Ultra is co-dominant with respect to Amel. Cornsnakes het for amel and het for ultra show an appearance that's partway between amel and ultra.""
...................................................................

Ahh..so a co-dominant gene is really two hets on the same locus that only partially express themselves. One is not dominant over the other.
Makes me wonder how much of the albino gene is expressed and how much of the ultra gene is expressed. Can the amount of expressions vary with individuals?

...Out of a clutch of 10 snakes this year, I got 4 gold dusts and 2 ultramels. Some of them were definitely brighter than others, and it was not gender related. I don't know whether this is another unknown gene in the mix showing up, or just natural variation though... I hesitate to label it as one or the other with only one clutch's worth of data.
-Kat
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"You keep WHAT in your freezer?"
"Mice. And rats. If that bothers you, I can call them 'cows' instead."

i know what an ultramel is but whats an ultra look like?
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jake

my addiction:
2 normal ball pythons (lazlo and izzy)
1 amelenistic corn snake (mazy)
0.1 blizzard corn (blizz)

Pretty darn hard to distinguish an ultra from a regular hypo A. It's the ultramels that are the phenotypically interesting ones.
-Kat
-----
"You keep WHAT in your freezer?"
"Mice. And rats. If that bothers you, I can call them 'cows' instead."