XI COUPLING AND REPULSION 123 



The Fj generation should consist of the four 

 classes purple long, purple round, red long, and 

 red round in the proportion 129 : 63 : 63 : i. In 

 other words the first three of the four classes should 

 be found closely in the ratio 2:1:1, while the 

 remaining class, the red rounds, should only occur 

 once in every 256 plants. The experimental figures 

 given in the scheme on p. 122 show that this 

 condition is closely fulfilled. 



In considering these two series of experimental 

 results together, there is one feature which stands 

 out prominently. In each case the majority of 

 the gametes produced by the F^ plant are of the 

 same kind as the two gametes through whose union 

 the plant itself was formed. The F^ plant formed 

 by the gametes BL and bl gives rise to seven times 

 as many gametes of these two types as of the types 

 Bl and bL. The Fj plant formed by the gametes 

 Bl and bL gives rise to seven times as many gametes 

 of these two types as of the types BL and bl. 

 And this is true of other cases where this peculiar 

 interrelation of the factors has been investigated. 

 In all such cases the plant which is heterozygous 

 for the factors showing this relation, produces a 

 majority of gametes of the two parental types. In 

 the earlier days of the study of this phenomenon 

 it was customary to speak of it in terms of the 

 " coupling " and " repulsion " of factors. When the 

 nature of the cross was such that both of the factors 

 B and L entered from one parent, and neither of 

 them by the other parent — when the cross was of 

 the nature BL X bl — the factors B and L were said 

 to exhibit partial coupling. In the formation of 



