Some Apparent Exceptions 89 



of these several possibilities will make them 

 clearer. 



When several factors enter into the pro- 

 duction of one character, the phenomena of its 

 inheritance are often apparently very compli- 

 cated. Thus coat color in rabbits is due to the 

 interaction of seven separable factors, three of 

 which have to do with the production of color, 

 three with its distribution, and one with its 

 intensity. Possibly the factors are chemical 

 substances whose reactions produce the appar- 

 ent effects on the coat color. That is mere 

 hjrpothesis; since we cannot tell just what they 

 are, they are designated by letters. The color 

 factor, C, must be present to have any color at 

 all. If absent, the rabbit is white, an albino. 

 B is the factor which acts on C to produce 

 black, Y, a factor which acts on C to produce 

 yellow. The yellow is obscured by the black 

 which overlays it if the factor B is present. E 

 is an extension factor, acting on black pigment 

 to spread it over the entire body. If this factor 

 is absent, only the eyes and the skin of the feet 

 are pigmented. U is called the uniformity 



