THE 



AMERICAN NATURALIST 



Vol. XLVIII October, 1911 No. 574 



SEX- -LIMITED AND SEX-LINKED INHERITANCE 



PROFESSOR T. H. MORGAN 

 Columbia University 



Darwin used the expression "inheritance as limited by 

 sex" to include all cases in which a character is peculiar 

 to one sex. His list of such cases covers in the main the 

 group of secondary sexual characters. Darwin's expres- 

 sion has been contracted to sex-limited inheritance, and is 

 widely employed to-day in the same general sense in which 

 Darwin used the expression. For instance, Bateson in 

 his book "Mendel's Principles of Heredity" includes 

 both horns in sheep and color blindness in man as sex- 

 limited characters. 1 



Now that the inheritance of several of these cases has 

 been definitely worked out, it has become increasingly evi- 

 dent that such characters as color blindness, and hemophi- 

 lia in man, the twenty-five "sex-linked" characters in Dro- 

 sophila, and certain characters in birds and in butterflies 

 follow a law of inheritance that is essentially different 

 from that followed by some of the other cases. It has 

 become necessary, therefore, to recognize two groups of 

 cases that differ fundamentally in regard to their heredity. 

 To one of these groups I have applied the term sex-linked 

 inheritance, and, for the present at least, we may still make 

 use of the older expression sex-limited inheritance (and 



* See pp. 169-174 in section headed " Heredity Limited by Sex; the Horns 

 577 



