92 



MENDELISM 



and this at present is by no means clear, it is now evident 

 that they will both ultimately take their place in some 

 common scheme. The relations between the two types of 

 series may perhaps be more clearly shown in the subjoined 

 table which brings out several points of interest in connec- 

 tion with them. The series marked with an asterisk are 

 those which have already been demonstrated experimentally. 

 The middle term in the table, in which all four kinds of 

 gametes are produced in equal numbers, is, of course, that 

 of a simple Mendelian case where neither repulsion nor 

 coupling occur. 



As the table shows it is possible to give generalised expres- 

 sions by means of which the nature of the generations 

 resulting from any of the series can readily be calculated. 

 The table brings out clearly the reason why repulsion at 

 first appeared to be absolute, for as its intensity increases 

 the zygote exhibiting both recessive characters rapidly 

 becomes exceedingly rare. Even for a series of such com- 

 paratively low intensity as A£ : 1 5 ^^ : 1 5 a£ : ab the ex- 

 pected proportion of aabb zygotes is only i in 1024, while 

 for a series on the i : 127 basis it is only i in 65,536. 

 A question of interest is whether the coupling and re- 



