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Discussion Starter · #1 ·
So, as far as I understand it, umbrous is a dominant gene, but only shows up in heterozygous agouti, right?

Here's my question: would a mouse like A/a e/e U/* still show the umbrous darkness on top?
 

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Yes, that's right.

A mouse who is A/a e/e U/* would still show umbrous. But, because e/e "washes out" all the black pigment, it will be a lot less than if it weren't also e/e. Sometimes you'll see e/e described as "sooty," meaning it has a deep brownish tinge all along its back. I think this is due to umbrous.

Umbrous is semi-dominant, but does not always show up because it is also a "dominance modifier" to agouti. In other words, when umbrous is heterozygous (U/u) and when Agouti is heterozygous (A/a, A/at, A/ae, Aw/a, Aw/at, or Aw/ae), the presence of umbrous modifies the dominance of whatever is on the A-locus with Agouti.

This means that a mouse who is A/a U/u will be agouti, but its back will be non-agouti, because the umbrous has "modified" the dominance of Agouti.

Here's a picture of umbrous on an agouti mouse:



You can see how the agouti (JM Sista)'s back is black. She is Aw/a U/u (umbrous white-bellied agouti carrying black).

Here is a picture on an argente mouse (the black part is diluted to dove):



This is WNT Langlia, bred by Jenny, owned by me and now living in retirement with Kadee. She had an extremely wide gray band and it got grayer with age.

There's an article published in the Journal of Genetics in the 1940s that has a lot of info on umbrous, its inheritance, and its expression. I forget the title of it, though, and google didn't turn anything up...

Edit: here it is: http://www.ias.ac.in/jarch/jgenet/40/229.pdf
 

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Discussion Starter · #3 ·
Okay, because I bred a mouse that was either poor brindle or sooty RY to at/a, and none of the babies are brindle, but three of them are agouti, 4 are black, and 3 are PE without any markings yet, so I was wondering if that meant she was A/a e/e U*. So the umbrous only shows up if BOTH agouti and umbrous are heterozygous? So far as I can tell, none of the babies show umbrous...
 

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Discussion Starter · #7 ·
Since the three agoutis so far just look normal, I think they might be u/u, assuming the mother is A/a e/e U/u, since it shows up quite strongly despite the e/e. Two of the blacks are at/a. I'll take a closer look at the other two blacks, see if they're really agoutis under the disguise of umbrous.
 

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Jack good explaining.... I love umbrous When you have a PEW or a BEW you can have also a Umbrous it looks very nice...but only when you have A- mit self it do not work .... The umbrous are not change during a molt... i have never see that...
This is a Aa ee Uu mice... he is not so red because he have no bb....


AA C c(ch) Uu mice


Aa ee UU


And this is not UU ....it is a Ay with smut this is a old pic....he get fat when he was 6 months old...because he have the Ay...I don't breed that now...


And you see good the difference between Uu and UU....UU have a color gradient... you see that when you blow in the coat... Ticking and no ticking places...
 

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Discussion Starter · #11 ·
My Dawn (the one I've been talking about) looks a lot like the first picture, except a little less red. There are four blacks, four agoutis, and three PEW in the litter, and none of the agoutis show any sign of darkening, and they're 10 days old. I noticed yesterday that Dawn looked like she was molting, and while it didn't look like the dark area had changed, I could see a definite molt line (not as bad as yours, Jack!). The line was equal on the dark and light areas.
 

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Umbrous is its own allele. It's dominant and represented U/U (homozygous umbrous), U/u (heterozygous umbrous) or u/u (homozygous non-umbrous).

It's more common in some lines of show mice, I think (particularly PEW, where it "hides"), although it does pop up in petstores and probably even in the wild.
 
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