SHORTER ARTICLES AND DISCUSSION 



PINK-EYED WHITE MICE, CARRYING THE COLOR 

 FACTOR 



Among the many domesticated varieties of the house mouse 

 {Mus musculus), two sorts with entirely white pelage are known, 

 —the albino, and the black-eyed white. Numerous experiments 

 have shown that the albino differs from colored varieties by the 

 loss of a single factor, the color factor ; for, in crosses with colored 

 varieties, albinism acts as a recessive allelomorph. The genetic 

 composition of the black-eyed white is less well known although 

 several hypotheses have been suggested. Black-eyed whites pos- 

 sess the color factor as crosses with albinos have shown. They 

 may be homozygous in the factor for dark eyes. A black-eyed 

 white male produced 189 dark-eyed offspring in my experiments 

 when mated to pink-eyed intense brown females. The offspring 

 of this cross were heterozygous in dark eye (Dd). By mating 

 them inter se, pink-eyed forms were obtained in the F 2 genera- 

 tion, some of which had a pure white coat. In other words, it is 

 possible to recombine the factors producing the pure white pelage 

 of the black-eyed whites with the pink-eyed condition. Such pink- 

 eyed whites resemble true albinos in appearance, but not in zy- 

 gotic constitution, for they still retain the color factor although 

 they show no color. To avoid confusion in discussion, I shall 

 refer to this synthesized form of albino as a pink-eyed white to 

 distinguish it from the albino lacking the color factor. Predic- 

 tions often compel subsequent retractions ; however, I feel safe in 

 predicting colored offspring from a cross between the pink-eyed 

 white and the albino, although externally the mating resembles 

 a cross between albinos which always breed true. Black-eyed 

 white strains sometimes show a few colored hairs around the ears, 

 between the eyes, and in front of the tail. The corresponding 

 pink-eyed white forms may also show the same characteristic. 



The white coat and pink eyes of the albino mouse are due to the 

 loss of a single factor; but the white coat of the black-eyed 

 white strains cannot be accounted for in such a simple manner. 

 Little ( '13) seemed inclined to the view that the black-eyed white 

 mouse was a spotted individual in which the spotting was of the 

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