68 



A MANUAL OF MENDELISM 



Considering their sources, the Wn data contain 

 probably the smallest proportion of inaccuracies. 



Professor Wentworth has suggested that there are 

 two pairs of factors operating to produce whites, reds, 

 and roans, namely, red and its recessive white, and roan 

 pattern and its recessive plain. If this theory be correct, 

 there ought to be four groups, as follows : 



Red 

 Roan 



9 



Red 

 Plain 



White 

 Roan 



White 

 Plain 



On this theory, the roans and the whites should both 

 be more numerous than they are, and reds should 

 produce reds and whites in the proportion not very 

 much less than 3:1. At the same time, since some of 

 the red roans should be pure not only for red but also 

 for roan pattern, the mating of red roan with red roan 

 should produce red roans to reds in even higher propor- 



