CHAPTER XVI 



THE INHERITANCE OF SEX 



In the previous chapter the manner in which the 

 practice of breeding will probably be modified by 

 the dissemination of the main conclusion which flows 

 from Mendel's work was indicated. In the present 

 chapter a theme of mere academic interest will 

 engage our attention, namely, the application of 

 Mendelian principles to the question whether there 

 is a fundamental and constitutional — to be absolutely 

 precise, a zygotic — difference between the sexes. 



One of the most recent, and certainly the most 

 interesting, of the applications of Mendelian prin- 

 ciples consists in the attempt to interpret the pheno- 

 mena of sex by means of these principles. But 

 before this theory is described it is necessary to 

 present certain cases in which the normal course 

 of Mendelian inheritance is disturbed by the inter- 

 ference of sex. 



A horned breed of sheep — the Dorset Horned — 

 in which the horns are well developed in both sexes, 

 was crossed* with a hornless race, such as the Suffolks, 

 both sexes in which are hornless. The result was that 

 all male lambs of the first hybrid generation developed 



* Note on the " Inheritance of Horns and Face Colour in Sheep." — 

 Journ. Agric. Sci,, vol. i., pt. 3, p. 364. 



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