GENETIC SYSTEM: RELATION TO CHARACTERISTICS 93 



was present). Sons were produced by the union of ova that 

 contained no X with sperms that carried X; this gave sons 

 XO, with their single X from the normal father, instead of 

 from the mother, as is usually the case. And such sons had 

 the normal gray body color of the father, instead of the 

 yellow body color of the mother, as happens normally. 



Thus with a change in the distribution of the X's there is 

 a corresponding change in the method of inheritance. If the 

 sons receive their X from the recessive mother, as in the 

 normal cases, they are recessive like the mother. But when, 

 through non-disjunction, the sons receive a dominant X 

 from the father, they are dominant like the father. Simi- 

 larly, in the normal case the daughters receive a dominant 

 X from the father and are therefore dominant like the 

 father. But in cases of non-disjunction the daughters re- 

 ceive both their X's from the recessive mother, and are 

 therefore recessive like the mother. In sum, when the X's 

 are normally distributed, such matings give "criss-cross in- 

 heritance" ; sons like the mother, daughters like the father. 

 But when the X's are not so distributed, there is no criss- 

 cross inheritance; sons are like the father, daughters like 

 the mother. The dominant and recessive characters follow 

 the respective X-chromosomes, whether these are distrib- 

 uted normally or abnormally. 



Such experiments have been repeated many times, and 

 with other sex-linked characters. Always the characteristics 

 follow the distribution of the X-chromosomes, however 

 these are distributed. 



It may be concluded with certainty that it is the presence 

 of X-chromosomes of a modified type that causes the ap- 

 pearance of the particular sex-linked characters that are 

 manifested. The rules of distribution of sex-linked charac- 

 ters are the rules of distribution of the X-chromosomes. 



