DUNN — UNIT CHARACTER VARIATION IN RODENTS 
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albino and its dominant allelomorph ruby-eyed dilute, in which the 
reduction of the melanic pigments is visible in the generally lighter 
tone of black, coupled with a complete absence of yellow. In the 
guinea-pig three graded variations have occurred: (1) dilution^ re- 
sulting in a reduction of all pigments; (2) ruhy, resulting in the absence 
of yellow, and the further reduction of black and brown in fur and eyes 
to very light shades (probably homologous with the ruby variation in 
rats); and (3) Himalayan albinism, which determines the absence of 
yellow and the restriction of black and brown to the extremities, ears, 
nose, feet, and rump, while the eyes are pink. These three conditions 
are distinct in appearance, do not blend in crosses and are all alterna- 
tive allelomorphs with full color and with each other. No complete 
albinism is known in the guinea-pig. In the rabbit two changes have 
taken place: Himalayan albinism (probably homologous v/ith the 
Himalayan albinism of guinea-pigs) and 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 generation 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 occurrence of this variation in 
several species, its similarities in appearance and in inheritance, and 
finally the production 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 different 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 al- 
binism is homologous variation throughout the rodents and in the 
species studied is due to homologous genes.® 
PINK-EYE 
This name has been appfied by geneticists to a unit character in 
rodents which is not a form of albinism, as the pinkness of the eye 
might indicate, but a distinct eye and fur character. Animals ex- 
® 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 differs from the wild gray or “agouti” coat color in the absence of yellow, and 
its replacement by white, and in the reduction of black to a slate blue. 
