98 



the Himnlayan albinism of guinea- 

 pigs) ai:J albinism. These are allelo- 

 morphic with full color and with each 

 other; that is, crosses of full colored 

 animals with albinos produce only full 

 colored young and in the second gen- 

 eration only colored and albinos. The 

 same is true of the cross colored X 

 Himalayan, while the cross Himalayan 

 X albino produces only Himalayan 

 and in the second generation only 

 Himalayan and albino. The occur- 

 rence of this variation in several 

 species, its similarities in appearance 

 and in inheritance, and finally the pro- 

 duction at the same locus as indicated 

 by allelomorphism of other similarly 

 appearing variations indicate that the 

 particular locus in the chromatin at 

 which these mutations have occurred 

 is common to a number of widely dif- 

 ferent species and although such a 

 statement cannot be proved except by 

 a study of linkage relations between 

 this and other common loci, it seems 

 very probable that albinism is homol- 

 ogous variation throughout the ro- 

 dents and in the species studied is due 

 to homologous genes.^ 



PINK-EYE 



This name has been applied by gen- 

 eticists to a unit character in rodents 

 which is not a form of albinism, as 

 the pinkness of the eye might indi- 

 cate, but a distinct eye and fur char- 

 acter. Animals exhibiting this variation 

 show a general quantitative reduction 

 in the black and brown pigments in 



•^ Since this paper was written, a fourth 

 allelomorph in the albino series in rabbits has 

 been reported by Castle (Science, vol. 53, 

 April 22, 1921, p. 387). This variation, now 

 studied genetically for the first time, is 

 known as "chinchilla" and diflFers from the 

 wild gray or "agouti" coat color in the ab- 

 sence of yellow, and its replacement by 

 white, and in the reduction of black to a 

 slate blue. 



DUNN 



both fur and eyes. A certain amount 

 of pigment is present in the iris but 

 not enough to obscure the blood color 

 of the retina. Yellow pigment is not 

 affected. Pink-eyed animals with the 

 "agouti" coat pattern therefore appear 

 yellow since the black bases of the 

 dorsal hairs are a reduced slaty or 

 bluish tint and are covered by the fully 

 intense yellow parts of the hair. Black 

 animals with this variation are slaty or 

 bluish all over in mice and a dirty 

 near-white in rats and guinea-pigs. Its 

 distinctness from albinism becomes 

 evident when pink-eyed colored ani- 

 mals are crossed with albinos. The first 

 generation offspring in this case are 

 all as fully colored as the wild type 

 and if inbred produce full colored, 

 pink-eyed colored, and albino young. 

 The variation occurs in the follow- 

 ing species: 



Sciuridte — *Marmota monax 

 Murid<£ — Mus musculus 



Rattus norvegicus 



*Microrus pennsylvanicus 



*Fiber zibethicus 

 Caviidce — Cavia cobaya 



Its occurrence in the species marked * 

 is probable but is based only on mu- 

 seum specimens with the coat colors 

 peculiar to pink-eyed animals. The 

 eyes in the mounted specimens may or 

 may not agree with the original. 



Data on the localization of this vari- 

 ation are available in large numbers 

 for mice, and in lesser amount for rats 

 and guinea-pigs. In these species it is 

 a simple Alendelian recessive to full 

 color (dark-eye). In rats and mice it 

 is certainly a homologous variation, 

 in appearance, in inheritance and in 

 localization, for a large amount of 

 linkage data indicates that the genes 

 for pink-eye and for albinism are 

 located in the same chromosome and 



