SEX INHERITANCE 



109 



In certain sheep, such as some races of Merinos 

 (Fig. 36 A), the horns are present only in the ram. 

 If a young ram is castrated his horns fail to grow. 

 To study the inheritance of the factors involved in 

 this difference it would be necessary to use for 

 crossing with Merinos a different breed in which 

 the horns were present (or absent) in both sexes, 

 but such an experiment has not been made. There 





Fig. 3GA. — Merino sheep of Ranibouilk-t. Ram horned, ewe hornless. 



are other breeds of sheep in which both sexes are 

 hornless (Suffolks), and still other breeds in which 

 both sexes are horned, those of the ram being 

 larger (Dorsets) (Fig. 36 B). The two latter have 

 been crossed. It may be that we are dealing here 

 either with factors for horns different from those 

 in Merinos, or that modifying factors cause the 

 different conditions. In this cross (Fig. 36 C) 

 therefore it can not be said that we are studying 



