194 UNIVERSITY OF MISSOURI BULLETIN 



are white. More curious still, when these whites of the 

 second generation are bred among themselves, they will pro- 

 duce nothing but pure whites and their offspring will have 

 no more taint of the gray than had the whites used in the 

 original cross. It is this "segregation" of characters which 

 is the essence of Mendelism, not the phenomenon of 

 dominance. 



A similar phenomenon is found in the case of the gray 

 character, though it is not apparent in this generation, being 

 obscured by the dominance of the gray over the white. It 

 becomes evident, however, when we study the progeny of the 

 individuals comprising the 75 per cent of gray animals, of 

 which there are really two kinds : namely, one-third (or 25 

 per cent of the entire generation) pure grays and comparable 

 to the pure whites, since they give only pure grays when bred 

 inter se, and two-thirds (or 50 per cent of the whole) impure, 

 since they yield both gray and white offspring. From the 

 middle 50 per cent of the second generation there will again 

 arise pure grays, hybrid grays and whites in the same ratio, 

 and this may be continued indefinitely. In every subsequent 

 generation we can "extract" the pure grays and pure whites, 

 leaving a balance of gray hybrids in which the white character 

 is recessive. 



You will see at once that these results are quite sub- 

 versive of the whole notion that purity of breed for any 

 character depends upon the length of the line through which 

 the character can be traced in all the ancestors of a g^ven 

 individual, for here is a pure white individual one-half of 

 whose grandparents were pure gray. 



You could, if you chose, carry out the scheme to many 

 subsequent generations. Suppose then, you were to take one 

 of the hybrid gray animals (the middle 50 per cent in the 

 hundredth generation. It would be to all appearance gray, 

 though it could be demonstrated to be a gray-white by the 

 offspring which it w^ould produce. Traced back through the 



