Inheritance in Gametophytes 127 



allelomorphs (A and a). It will be recalled that such a 

 pair of allelomorphs may behave in two different ways in 

 hybrid sporophytes. In case of complete dominance, 

 A alone will be expressed in the hybrid A a. In case of 

 lack of dominance or of only partial dominance, the 

 hybrid Aa will partake of the nature of both A and a; or, 

 in other words, it will be a blend, intermediate between 

 the two pure parents A A and aa. 



A similar situation may be considered in the game- 

 tophyte generation. In a gametophyte, A can be 

 present or a, but not both. Here at least is a case of 

 presence and absence about which there is no doubt. 

 In this case there would be invariably pure dominance, 

 or what corresponds to it, but there could not be a blend. 

 It is interesting to consider the results of this situation. 

 If in a study of inheritance in gametophytes cases of 

 pure dominance only are discovered the result is quite 

 consistent with our theories. If, on the other hand, 

 cases of blending inheritance are discovered what are to 

 be the conclusions ? The only possible conclusion would 

 be that our theoretical mechanism is wrong; that 

 chromosomes are not the bearers of hereditary characters, 

 or at least not the only bearers; or else that the behavior 

 of the chromosomes at the reduction division is different 

 from that which cytologists and breeders have long 

 supposed. In other words, we have here a chance to 

 test the doctrine of segregation through the reduction 

 division. 



The case of complementary factors may also be 

 considered. Recalling the behavior of complementary 

 factors in the sporophyte generation the question arises 

 about their behavior in the gametophyte generation. 



