No. 524] CHROMOSOMES AND HEREDITY 473 



in-' between the hybrid (Fj) with the recessive (fourth 

 line) ; and with dominant (fifth line). They give the 

 ex i leeted proportions. 5 



In all of the preceding cases except the first the 

 gametes are not pure, as a rule, but nevertheless pro- 

 duce two classes of individuals that may be sharply de- 

 fined. This scheme seems to work as well as the pure 

 gamete assumption; it avoids certain difficulties encoun- 

 tered by the latter; and appears to explain further a 

 class of cases inexplicable on the pure gamete hypothe- 

 sis; namely the graded series of forms so often met with 

 in experience and so often ignored or roughly classified 

 by Mendelian workers. 



Again, for simplicity it lias been assumed that varie- 

 ties or races lacking a character lack entirely the kind 

 of activity that calls forth that character. But there is 

 no need to make this limitation. If in some cases the 

 lack of character may in reality be due to total absence 

 of action, there are other cases which can be explained 

 on the chromosome basis if we assume that the absence 

 of a character is due to incomplete or insufficient activ- 

 ity of its chromosomes varying from 1 to 50, to put the 



itv takes place. Such an individual paired to a' domi- 

 nant will give dominance in the first generation (due to 

 the 50 per cent, of the dominant plus 25 per cent, of the 



gametes, but one class will contain numerically more than 

 50 per cent, of character-forming materials. Conse- 

 quently there will be more individuals of the dominant 

 race than the theory of pure gametes and equal division 

 demands. 



The converse case is also worthy of consideration. If 

 one individual is just able to produce a given color or 

 material by the combined activity of its two chromo- 

 somes, but no more than just able to do so, and the other 



