Chapter 4

Dilute and Leaden, the p-Locus, Ruby-Eye, and Ruby-eye-2

IV. Ruby-Eyed-2 (ru-2)

A. Origin and Description

In 1966 Lilly reported a recessive coat-color mutation which, because it was phenotypically identical to ruby-eye, he designated ru-2. The deviant occurred in a substrain of C57BL/6 and was shown to be located near pink-eyed on chromosome 7. Eicher ( 1970a), in a more detailed linkage analysis, reported ru-2 to reside 3 cM from p and 17 cM from c with the order being c— p— ru-2. Like ru, ru-2 produces a grayish-brown color in the eumelanin region of the agouti hair and dark red eyes. ²² Phaeomelanin is only slightly affected. The influence of ru-2 at the cellular level has unfortunately not been investigated ( Eicher, 1970a).

B. Other Alleles (Maroon and Haze)

Recently it has been discovered that maroon ( mr) and haze ( mr^hz), two recessive coat-color determinants which were believed to be inherited independently from ru-2, are actually allelic with ru-2 ( Eicher and Fox, 1977). Hence these two mutants are now designated ru-2^mr (maroon) and ru-2^hz (haze).

Maroon arose spontaneously in a "lactation" stock ( N. Bateman, 1957). The eyes of ru-2^mr/ru-2^mr mice are colorless at birth, but darken to a rich maroon. The coat color of maroon mice varies from almost normal to extreme pallid, even among sibs, and darkens with age. The underfur and isolated hairs of this mutant are often silvered ( N. Bateman, 1957). According to Roderick ( 1973, 1975), nonagouti maroon ( a/a;ru-2^mr/ru-2^mr) animals look very much like nonagouti buff ( a/a;bf/bf) mice (see Chapter 6, Section IV, B). Nevertheless, these mutants can be readily distinguished from each other by the fact that whereas a/a;ru-2^mr/ru-2^mr mice have light ears, a solid belly, and translucent eyes, a/a; bf/bf animals have darker ears, a belly lighter than the rest of the coat, and opaque eyes ( Davisson, 1977). According to Davisson "the eyes must be observed by examining the mouse in profile against light." the double homozygote a/a;ru-2^mr/ru-2^mr;bf/bf has a distinctly lighter coat color than either homozygote alone ( Roderick, 1975; Davisson, 1977). Maroon has been reported to interact with silver ( si) in the F₁ ( N. Bateman, 1957) (see also Chapter 6, note 11).

Haze was originally described by Dickie ( 1965b) after it arose spontaneously in the DBA/2J strain. This mutation is characterized at birth by light colored eyes. In the adult the hair color is brownish and the ventrum is white. In 1974 E.S. Russell demonstrated that haze was allelic to maroon.