MULTIPLE ALLELOMORPHS 161 



colors, although the others may to some extent 

 appear, especially in old mice. The third allelo- 

 morph produces only black or at least the chocolate 

 pigment, if present, is obscured by the darker color. 

 Finally, the fourth allelomorph produces gray on 

 the back and sides while the belly is pure white 

 (the under hair is black). This series illustrates 

 how allelomorphs of the same locus may not only 

 determine the color, but also act to determine where 

 a color is to develop. The allelomorphs differ there- 

 fore in regard to what part of the body they affect, 

 or the time in ontogeny when they act, as in the 

 banded hair of the gray mouse. 



This case serves, therefore, as an excellent intro- 

 duction to the cases that Emerson has described in 

 corn (maize), in which the red color of the grain 

 (pericarp), cob, silk, and husk furnish a wonderful 

 series of character combinations that can be ex- 

 plained on the multiple allelomorph hypothesis. 

 Emerson adopted the hypothesis of complete linkage, 

 but the same arguments as used in other cases lead 

 us to prefer the alternative of multiple allelomorphs. 

 In some varieties of corn the grain, the cob, the silk, 

 and the husk are all red; in others, all white; in others 

 the grain may be red, the cob, silk, and husk white; in 

 others, the grain may be white and the rest red. 

 Practically all possible combinations are known, and 

 so far as tested the combinations that go in through 

 the two parents come out in F 2 according to expecta- 

 tion, i.e., they give no new gametic recombinations. 

 If we assume that there is a system of allelomorphs, 



