Color genetics question

[SarahMelisse]

Which gene creates Tortiseshell? Is it part of the En gene for brokens?

Also, I bred my REW to my Fawn FA and one of the possible outcomes is tort marten... What color is that? I googled it to see, but there are some pictures where it is a a red/orange and some where it's a black color.

One more: Is it possible for a REW to mask an "A" or "at" agouti gene? Or will a REW always be "aa"?

 

[Bunnylady]

Tort is caused by the non-extension allele, which is one of the alleles in the E series. It has nothing to do with En, the broken gene.

The E series is as follows:

Es - Steel

E - Normal extension

e - non-extension

ej - harlequin

(Some say there is another allele in the series, Dominant Black, but I think the jury may still be out on that one)

The non-extension allele reduces the amount of black that is present in the hairs on the rabbit's coat. On an animal with the agouti (A) allele in the A series, this results in a red or orange. On an animal with two self alleles (aa), the result is a tort. A tort marten would have the tan-pattern allele (at) as its most dominant allele in the A series. Tans have the light eye rings, nose markings, light belly, ear lacing, etc. of an agouti, with the body coloring of a self. A tort marten would look like a tort (reddish body, with almost black on the ears, face, feet, tail and sides) and have the lighter "trim" of an agouti.

REW is the color that results from a rabbit inheriting two copies of the most recessive allele in the C series. There is no way visually to know what the REW has in the A, B, D, E, En, etc. series, because cc (REW) effectively removes all color from all areas of the coat. So yes, REW rabbits can have agouti or tan alleles. I once owned a Holland Lop that I called a "broken REW," because she threw broken babies when bred to a solid buck. She had the broken allele (En), but of course you couldn't see it.

Hope that helps!

 

[SarahMelisse]

Thank you so much for clearing that up for me! Unfortunately my rabbits have a REW in every generation so it has been pretty hard to tell from the pedigree what some of them are hiding... It would be nice to know what some of the litter mates looked like.

Is fawn a dilute or non-extension of red/orange? And is red/orange an "A_B_" always... meaning, is red/orange an agouti form of black?

Sorry if I'm being so specific on these color genetic questions, but it seems all the sites with information are really general. If anyone knows a site or book with a more in-depth look at rabbit coloring, please let me know!

 

[Bunnylady]

Exactly what a "fawn" is, depends on the breed. Usually it is genetically a dilute orange (A_B_ddee), though I have read a description of it in at least one breed that clearly cannot be (though which breed, I can't remember at the moment). Red/orange is always an agouti color, though it isn't always of black. The non-extension allele frequently doesn't remove all of the dark pigment from the tip of the hair in an agouti, which can leave a lot of "smuttiness" on a red. The "best" reds have chocolate alleles at the B locus. Because brown isn't (visually) that far from orange, whatever eumelanin is left on the tip of the hairs is much less noticeable, and the resulting color is brighter.

 

[SarahMelisse]

Ok.. So red/orange is always agouti (A) but can be either black (B) or brown (b). I think I'm starting to get the hang of this. Thank you for the information!