124 MENDELISM chap. 



gametes by the F^ plant, they tended to enter 

 into the same gamete seven times as often as they 

 entered into different ones. So also when the cross 

 is of the nature Bl x bL the Y^ plant is of the same 

 constitution, viz. BbLl. But the majority of the 

 gametes formed are of the nature Bl and bL. The 

 two factors pass into different gametes seven times 

 as frequently as they enter into the same one. 

 During the gametogenesis of the F^ plant they 

 appeared to repel one another, though not in every 

 case, whence originated the term partial repulsion. 

 At the time when these terms were proposed it was 

 not understood that both coupling and repulsion were 

 essentially part of the same phenomenon. More 

 recently the term " reduplication " has been brought 

 into use. In the gametic series 7 BL : \ Bl : 

 I bL : "J bl the terms BL and bl are said to be 

 reduplicated : in the series i BL : y Bl : y bL : i bl 

 reduplication is shown by the terms Bl and bL. 

 The term is not altogether satisfactory, for biologists 

 are not at present in agreement as to the manner 

 in which these gametic series come to be formed. 

 For the moment we may continue to use the terms 

 coupling and repulsion provided that we remember 

 they are essentially part of the same process. 



In the case of the factors which we have been 

 discussing, the preponderance of the parental types 

 of gamete was as 7:1. But it differs widely for 

 different characters even in the same species as the 

 following examples serve to illustrate. In some 

 sweet-peas the anthers are sterile, setting no pollen, 

 and this condition is recessive to the ordinary fertile 

 condition. Again there is a peculiar monstrous 



