126 WHAT EVOLUTION IS 



other two-thirds, or one-half of the 

 total, can be shown to be mixed, in 

 that, like their parents, they will 

 when bred together produce both 

 black individuals and white individ- 

 uals. The remarkable feature of 

 such breeding series is the regularity 

 with which the proportions, just 

 stated, occur. The occasion of these 

 remarkable Mendelian proportions 

 can be seen when such a series, as 

 that described, is analyzed. 



When opposing characters, such as 

 white and black, are combined in 

 breeding, as in the case of the guinea 

 pigs mentioned in the preceding para- 

 graph, only one of these characters 

 appears in the first generation of off- 

 spring, namely, in the particular in- 

 stance under consideration, black. 

 All guinea pigs in the first generation 

 after the cross white-black are black. 

 But these black individuals carry 



