MORGAN, COAT COLORS IN MICE 91 



might contain other colors than yellow and gray. Owing to the sterility 

 of the yellows, I have had poor success with this cross. Three litters 

 only of the F x yellow by yellow were obtained. They gave ten yellows and 

 two grays with white belly. In another case yellows were paired with 

 grays with gray belly (from Iowa). Two of the yellows that resulted 

 from the cross produced five yellows, five grays with gray belly and two 

 cinnamon agoutis. In all therefore the F x yellows have given fifteen 

 yellows and nine grays. 



These results, while not so extensive as I should wish, indicate that the 

 yellow-bearing germ-cell is pure for yellow in the sense that yellow is 

 allelomorphic to gray. In other words, yellow has for its allelomorph in 

 the hybrid with gray the combination of yellow-black- 1 chocolate that 

 stands for gray. Whether chocolate and black are separate factors, or 

 whether black is a development through chocolate, and if so whether an 

 independent factor (not contained in the complex) brings about this 

 change need not be discussed now, but will be examined later. Whichever 

 of these views seems more satisfactory, the results of this experiment, as 

 far as they go, show that the yellow-bearing germ-cell is pure for that 

 color factor. The numbers are not large enough perhaps to put the 

 matter beyond question. As far as they go, however, they indicate that 

 the yellow gametes of the yellow mice carry only yellow, and that gray 

 (and perhaps chocolate too) is allelomorphic to yellow. I lack the evi- 

 dence to show the nature of the yellow pigment in mice, whether it is a 

 lipochrome, as commonly assumed, or belongs to the melanin series. I 

 must rest my case on the experimental evidence that seems to show that 

 yellow is the allelomorph of gray (i. e., of the colors that go to make up 

 the gray). Since yellows may carry other colors latent, gray as well as 

 chocolate or black, but only gray (black-yellow-chocolate) when gray has 

 been introduced as such, either the ticking factor is a separate factor, or 

 else some special combination (union) of black, chocolate and yellow 

 exists which when present will give the ticked or barred condition to the 

 hair. It may seem more probable that the barring factor is a separate 

 factor that behaves independently of the other factors and when present 

 produces its effect, except when dominated by the yellow factor. That 

 this factor may act with chocolate and black alone without yellow is indi- 

 cated below in the black-chocolate mice out of gray parents. 



The F x white-bellied mice were crossed extensively with mice of other 

 colors, and they produced white-bellied grays and other colors according 

 to expectation. Gray bellies also appeared among the progeny when yel- 

 lows were used, which is explained on the ground that the yellow mice 



1 The presence of black in this combination will be considered later. 



