SHORTER ARTICLES AND DISCUSSION. 



SIAMESE, AN ALBINISTIC COLOR VARIATION IN 

 CATS 



Comparative studies of color inheritance in mammals have 

 shown that pigment production throughout the group is due to 

 similar processes and to genes probably homologous. These 

 studies have shown, for example, that the pink-eyed albino con- 

 dition seen in white rabbits, white rats, white mice and white 

 guinea-pigs behaves in all cases as a simple recessive in crosses. 

 It is probably due to variation in the same (/. e., in an homo- 

 logous) genetic locus in all these rodents. In its usual form 

 albinism consists in a complete absence of pigmentation from 

 the ectoderm of the embryo and from all derivatives of that 

 germ-layer in the adult animal. This includes, not only th-? 

 hair, but also the retina and iris of the eye. Such is the condi- 

 tion seen in the white mouse, the white rat, and the "Polish" 

 or "Russian" rabbit. But this same locus may apparently 

 undergo a different change which, while it behaves as the per- 

 fect allelomorph of the pure white albino variation, differs from 

 it in that it allows a certain amount of pigment to be produced, 

 more particularly in the retina of the eye and in the hair at 

 the extremities of the body (nose, ears, tail and feet). At times 

 a small amount of pigment is formed elsewhere throughout the 

 coat. This condition is best known in the "Himalayan" rabbit. 

 Clear white albinism of the Polish rabbit is an allelomorph of 

 Himalayan albinism. In the guinea-pig only the Himalyan 

 type of albinism is known ; in rats and mice, only the Polish 

 type is known. 



In the guinea-pig, "Wright has demonstrated the existence of 

 two other albino allelomorphs, which apparently are distinct 

 mutations of the same genetic locus. These are found in the red- 

 eyed and in the dilute varieties described bv him. Among rats 

 Whiting and King have demonstrated the existence of a variety 

 comparable with the dilute varieties of guinea-pigs and which 

 they call "ruby-eyed." It behaves as an allelomorph of ordi- 

 nary albinism in crosses. 



White spotting of colored animals, sometimos called "partial 

 albinism," is an entirely different variation, du,' to variation in 

 a different locus. True albhiisni and spottinL^ may by suitable 

 crosses be made to coexist in the same individual. In this way 

 265 



