CHAPTER IV 

 ORIGIN OF SOMATIC SEX-CHARACTERS IN EVOLUTION 



IN his Mender s Principles of Heredity, 1909, Bateson 

 does not discuss the nature of somatic sex-characters 

 in general, but appears to regard them as essential 

 sex - features, as male OT female respectively. As 

 mentioned above, he argues from the fact that injury 

 or disease of the ovaries may lead to the develop- 

 ment of male characters in the female, that the 

 female is heterozygous for sex, and from the supposed 

 fact that castration of the male leads merely to the 

 non-appearance of male somatic characters, that the 

 female sex-factor is wanting in the male. He does 

 not distinguish somatic sex-characters from primary 

 sex-factors, and discusses certain cases of heredity 

 limited by sex as though they were examples of the 

 same kind of phenomenon as somatic sex-characters 

 in general. One of these cases is the crossing by 

 Professor T. B. Wood of a breed of sheep horned in 

 both sexes with another hornless in both sexes. In 

 the F! generation the males were horned, the females 

 hornless. Here, with regard to the horned character, 

 both sexes were of the same genetic composition, 

 i.e. heterozygous, or if we represent the possession of 

 horns by H, and their absence by h, both sexes were 

 Hh. Thus Hh$ was horned and Hh% was hornless, 

 or, as Bateson expresses it, the horned character was 

 dominant in males, recessive in females. Bateson 



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