MORGAN, COAT COLORS IN MICE 99 



affects the "white" belly-hair in exactly the same way as it affects the hair 

 elsewhere — all color is lost. 



As is known, the spotted condition affects all mice of whatsoever color, 

 whether yellow, gray, black or chocolate, in the same way. If a yellow- 

 spotted mouse is crossed to a mouse with uniform coat of gray, black or 

 chocolate the spotting disappears in the first generation and the uniform 

 coat is yellow in some of the offspring. If these yellows are inbred, the 

 spotting recurs, not only in some of the yellow offspring but in the other 

 colors as well. The spotted condition is not therefore associated with any 

 peculiar color, but affects all equally and can be transferred from one to 

 the other as stated above. If we interpreted the absence of color in the 

 spotted white areas as due to a factor that suppresses color in these parts, 

 it would follow that it affects yellow in the same sense in which it affects 

 black and chocolate, and the ticked condition of the gray also. On such 

 a view we might argue logically that yellow belongs to the same series as 

 the other colors, since it is suppressed by the same factor. Furthermore, 

 if, as is generally believed, the spotted condition is due to the loss of the 

 color producer, so that the color determiner can no longer act to make the 

 color, then we are equally led to the conclusion that the color producer 

 for yellow is the same as that for the other colors — a conclusion of some 

 general importance. 



Eeturning to the change in the white hair of the belly of the sport, 

 when a white spot crosses the white belly, it is evident that the effect is 

 due to the loss of the color producer, so that the hair is white to its base. 

 This view is, of course, in line with the interpretation of the white belly 

 as a ticked region. 



This leads to a consideration of the ticking or barring factor. Obvi- 

 ously it is the same sort of thing as the spotting factor, only it appears in 

 each hair instead of in different regions of the body. If we push our 

 hypothesis to its logical limits, we must conclude that when the cells that 

 form the hair are laid down, during the earlier divisions of the cell (or 

 cells) from which each hair arises, there occurs a series of losses in the 

 different cells, so that the terminal cell and its descendants have lost the 

 determiners for yellow and black, leaving chocolate, the next cell or cells 

 lose the determiners for chocolate and black leaving yellow, and the last 

 cell of the chain retains only the black determiner. Similarly in the 

 white belly, the outer cells of the follicle have lost the color determiner 

 either for yellow or black, or the color producer, while the basal cells re- 

 tain the determiner for black as well as the producer. Since yellow may 

 appear in the yellow-bellied race in the outer ends of the hair it appears 

 simpler to suppose that it is the color determiner that is lost. 



