162 MULTIPLE ALLELOMORPHS 



such that one affects one combination of parts, 

 another a different combination, the results find a 

 simple and consistent explanation. It may seem 

 strange at first that a factor may make the cob red 

 and not color the grain or husk, while another 

 allelomorph may make the grain and husk red but 

 not affect the cob color, but it is no more strange than 

 that one factor determines one distribution of the 

 pigment over the coat and even in each hair of the 

 gray mouse and another one determines another 

 distribution. 



Equally striking is the series of forms of the grouse 

 locust (Paratettix) that Nabours has recently studied. 

 Nine true breeding forms that are found in nature 

 were studied. They differ markedly in color pattern 

 (Fig. 52) but each color pattern behaves as a -unit in 

 heredity. The hybrid is in a sense intermediate, the 

 color characters of each parent being superimposed. 

 In fact Nabours finds that simple inspection of the 

 hybrid suffices to show which forms were its parents. 

 In the germ cells of the hybrid the two parental color 

 types segregate as units. The resulting F 2 types 

 are in the 1 :2 : 1 ratio. It is obvious, since only two 

 of the color types can exist in the same individual, 

 and since they separate in the germ cells, that the 

 condition of multiple allelomorphism is fulfilled. 



All Nabour's crosses relating to color pattern (with 

 some possible exceptions) follow^ the plan just out- 

 lined. The case at first sight appears unique in that 

 the color pattern of each type is complex in the sense 

 that different parts of the body are differently affected 



