HEEEDITY 



were then asociated together in the offspring; 

 but black from its nature dominated, because 

 white in this case is due merely to the lack of 

 some constituent supplied by the black gamete. 

 But when the cross-bred black individuals on 

 becoming adult form gametes, the black and 

 the white characters separate from each other 

 and pass into different cells, since, as we have 

 seen, gametes are simplex. Accordingly, the 

 eggs formed by a female cross-bred black are 

 half of them black, half of them white in char- 

 acter, and the same is true of the sperms 

 formed by a male cross-bred black. The com- 

 binations of egg and sperm which would natu- 

 rally be produced in fertilization are accord- 

 ingly 1BB:2BW:1WW, or three combina- 

 tions containing black to one containing only 

 white, which is the ratio of black to white off- 

 spring observed in the experiment. 



Now the white individual may be expected 

 to transmit only the white character, never the 

 black, because it does not contain that char- 

 acter. Experiment shows this to be true. 

 White guinea-pigs mated with each other pro- 

 duce only white offspring. But the black in- 



36 



