This article is from the WSSF 2007 AFRMA Rat & Mouse Tales news-magazine.

By Karen Robbins

Jennifer Erwin, e-mail
Q I’ve been corresponding with an European breeder of mice and over there Bone (what AFRMA calls Ivory) is c^e/c, PEW is c/c, of course, and BEW is c^e/c^e. She said she bred a BEW x PEW and got all Bone babies. I thought the only way to get BEW from c^e/c^e was on a red background, but maybe I’m mistaken. I did find on Finnmouse’s site this statement, “in most mouse standards, Bone is called ‘Cream.’” The breeder said the BEW, Bone, and PEW came from PEW and Silver Agouti lines which confuses me even further since Silver Agouti is A/A c^ch/c^ch.

I was browsing the AFRMA standards pages looking at Cream and Ivory, and was wondering if you would mind explaining the difference to me. I just don’t understand the difference between the two.

A BEW can’t be c^ec^e in the normal sense as c^ec^e is usually very dark (what England calls Stone/our Reverse Siamese or our Coffee; Beige is also c^ec^e but a lighter shade; it’s just a dark version of Ivory) unless it is on dominant yellow or recessive yellow (ee c^ec^e). If it is not on dominant/recessive yellow, it would be c^ec selected for whiteness. In the photos you sent of a Bone and a BEW, they look the same, so based on the usual genetics of this color, they are both the same but selected for more white for the BEW. When you breed c^ec^e to cc you get all c^ec. Most clubs just use c^ec on chocolate (Ivory/Bone) selected for very light/white for this version of BEW. England’s B.E. Cream/our Ivory is c^ec on a Chocolate background. You can get it on a Black background—I have one recent male that was Bb as he produced Black and Chocolate when bred with Champagne [he went back to my cross of old PEW English that was genetically Lilac (P.E. Black aa pp) with the new English B.E. Cream bb]. The problem with using c^ec for BEW is they tend to get darker/watermarks and won’t stay “white.” You could get BEW by c^ec with agouti plus black (A– B– c^ec) and they would still have the off white problem but wouldn’t get fat. BEW is usually either Marked with all markings bred off, from Variegated, c^ec^e on dominant yellow, c^ec^e on recessive yellow, or very light Ivory/B.E. Cream/Bone c^ec. Genetically when you breed Ivory/Bone/B.E. Cream with PEW you get Ivory and PEW. The only way you could get Bone/Ivory from Silver Agouti is if the Silver Agouti were carrying other things.

An Ivory (cec) owned by and photo by Karen Robbins.

I asked Nichole Royer (our genetics expert) for more details as I have never done a Silver Agouti to Ivory breeding and this is what she says about breeding Silver Agouti to Ivory and about BEW: “Recessive yellow eliminates all the black pigment from the coat and leaves just yellow pigment behind. c^ec^e eliminates all yellow pigment. So together that should give a BEW. I’ve never tried it, but logically that’s how it should work.

“Breeding Silver Agouti to Ivory would get some Agouti babies; however, if the Silver Agouti was actually Aa or Aa^t then it’s entirely possible to end up with Ivory/Bone. Silver Agouti could easily be Aa, and c^ch plus any of the alleles lower on the C locus will strip away yellow pigment (and dilute out the black slightly). Well, I should say any of the alleles other than c^h. Chinchilla with the white belly is Aa^t. Also, to truly get a really good Chinchilla you logically would aim for ‘c^chc^e’ or ‘c^chc.’ c^ch will leave the black pigments fairly dark, but carrying alleles lower down on the locus the red/yellow pigments should dilute even more than c^chc^ch. Thus, if you don’t assume the Chinchilla is AA c^chc^ch, but instead is carrying other things, then it is possible to get Ivory/bone. It’s not the combination I would breed ‘expecting’ to get Ivory/Bone unless you knew that your population of Chins happen to have been bred for that background.”

On your question on Cream vs. Ivory: Cream is for the Chinchillated Fawn A^y– c^chc^ch or Chinchillated Red A^y– bb c^chc^ch and that is what we had been showing prior to getting the English B.E. Cream, where the Ivory is for the “Beige” family c^ec (when these mice get “watermarks” or have moult marks, they can be streaked/blotched with Beige on them). England kept one standard and just changed what they show for that color—for the last many years it has been the c^ec mice, but in the beginning it was the Chinchillated Fawn/Red.

AFRMA’s Mouse Genetics book would be useful for you to have if you haven’t gotten a copy yet.

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