KUBY-EYED DILUTE GRAY RAT 63 



white. The larger hairs are white, while those of intermediate 

 and small size are white at the base and tip only. For the rest 

 of their length they have large yellow pigment granules. In the 

 non-agouti red-eyes, aa.rr, the hairs are almost entirely white 

 except for the yellow stain similar to that which occurs in white 

 rats. There may be a very slight amount of extremely dilute 

 sepia pigment in some individuals. 



The double recessive, ruby-red, CrCr.rr, expected in the F2 

 generation from the cross of ruby-eyed dilute gray by red-eyed 

 yellow should be practically white even in the presence of the 

 agouti factor, for the Albino type of dilution found in the dilute 

 gray eliminates yellow, while red-eyed yellow dilution elmiinates 

 sepia. It is also to be expected that the double recessive, ruby- 

 pink, CrCr.pp, will have white hair. 



SUMMARY 



A new Mendelian variety of the Norway rat known as ruby- 

 eyed dilute gray has been found near the Zoological Laboratory 

 of the University of Pennsylvania. The hair is light sepia at 

 the tip and grades to white at the base. The eye color is ruby. 



The new variation is recessive to intense pigmentation. When 

 the dilutes were crossed to black-hooded rats all the Fi indi- 

 viduals were intense and the Fo generation showed thirty-three 

 intense and fourteen dilutes. 



Ruby-eyed dilution is allelomorphic with albinism. The Fi 

 individuals, called fawns, are intermediate both in hair and in 

 eye color. Fawns when bred together produced eighty ruby- 

 eyed dilutes, one hundred and fifty-six fawns, and eighty Albinos. 



Ruby-eyed dilutes crossed with red-eyed yellow rats produce 

 rats of the wild type. The second generation shows evidence of 

 linkage of the two factors, since double recessives did not appear. 



No linkage is apparent with hooding or with non-agouti. 



In the agouti dilutes the sepia pigment is restricted to the tips 

 of the hairs. The non-agouti are more heavily pigmented. 



