# Modifiers



## Lilly (Nov 21, 2015)

What exactly are they and how do they work?

I keep reading in a lot of places both on here and on other sites for the marked varieties especially but for others too, you need to build up the right modifiers, outcrossing can result in random things because the outcross may not have the right modifiers and other such things, but what exactly are they and how do they work?

From what I have read modifiers seem to be responsible for getting the right shade of colour, the right amounts of marking in the right places and a whole host of other things and can seemingly be passed down, but just a bit confused about the whole thing since I cannot seem to find what they are lol


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## SamOfChaos (Nov 29, 2015)

Modifiers modify 
So you have mice of the same genetic background, lets say pied. One has modifiers that results in an almost black mice and a little white on the belly. Another has Modifiers that turns the whole mice almost white.
If you want Pied with much white but you only have the ones with the modifiers for little white you can breed as much as you want you cant get them to have this much white.
So even if mice have the same mutation and are genatically the same color because of the modifiers they can look pretty diffrent.

Modifiers also can be dominant, ressesiv etc. thats why sometimes its so difficult to get theright shape or the right set of markings.


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## Lilly (Nov 21, 2015)

Thank you for that explanation but the genetics lover in me wants to know more!

Are they separate genes that interact with the way pigment is shown/distributed, are they proteins that are formed by something else or is it more delving into epigenetics? Is there a list of known ones and their effects/dominance or is it more some kind of naming that breeders have come up with to explain differences and how some trains can be inherited even though the colour genotype is the same?


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## Laigaie (Mar 7, 2011)

Technically speaking, they're separate genes. I say that in the sense that they're like all the different points of inheritance that determine skin color in humans. We don't have any one single skin color gene. We have lots of genes that alter human skin color, and they're inherited in bits and clumps. So yes, they're genes. But they're tons of different basically untrackable genes not on the tracked loci. For spotting caused by s, they're called k-factors. Color modifiers are usually either altering phaeomelanin or eumelanin (red/yellow or black pigments). Does that kinda make sense? We track the big on/off genes with genotype, and modifiers are all the genes that have much more subtle effects.


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## Lilly (Nov 21, 2015)

That makes sense, thank you 

But one more thing in terms of selective breeding, lets take sam's example of pied where you have modifiers that make the mouse almost entirely white and not show much of the colour, would you be able to make much of a headway towards say 50/50 without getting outcrosses or would that be harder to do because the mice you have do not posses the correct K-factors to make their phenotype like that? (assuming they just did not posses anything but "all white")


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## Laigaie (Mar 7, 2011)

Like everything else, it depends.

If the mostly-white pair comes from a line of highly varied mice, you'll probably be able to make significant headway. There are probably more k-factors there than you're seeing, and so long as you make good choices from the three litters you'll get of your F1 cross, it's feasible. But if these mice come from a line that's very heavily inbred toward that high-white pattern, it's going to take a loooooot longer to get a low-white mouse.

The place you see this the most often with mice (at least in the US) is butt patches. Somehow, the k-factors that give a mouse a solid rump are either super common or super dominant. Whatever it is, I hear all the time about pied breeders who can't get rid of solid butts.


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