OPERATION OF THE GENETIC SYSTEM 65 



four) a female Is produced. When the number of sets of 

 autosomes exceeds the number of X's, there is a tendency 

 for males to be produced. Two sets of autosomes plus one 

 X gives the normal male. Three sets of autosomes plus two 

 X's yields a combination In which the proportional excess 

 of autosomes is not sufficient to produce complete maleness; 

 it yields intersexes. But when three sets of autosomes are 

 present with but one X, the scale is tipped too far In the 

 direction of maleness. Abnormal Individuals are produced 

 in which the characteristics that distinguish males from fe- 

 males are accentuated beyond the normal ; Bridges calls these 

 "super-males." And similarly, If three X's are present with 

 but two sets of autosomes, the balance is tipped In the op- 

 posite direction, and "super-females" are produced. 



We may summarize the special results of these observa- 

 tions as follows : 



( 1 ) Both autosomes and X-chromosomes take part In 

 determining the sex. Altering either class of chromosomes 

 changes the sex. 



(2) Which sex Is produced depends upon a balance be- 

 tween the number of sets of autosomes and the number of 

 X's. 



(3) A preponderance of the number of X's tends to pro- 

 duce females; a preponderance of the number of sets of 

 autosomes tends to produce males. 



(4) By altering the balance in ways not commonly oc- 

 curring, various intermediate and extreme conditions as to 

 sex are produced. 



4. Method of Operation of the Chromosomes in Producing 



Sex Differences 



The results just set forth are of great significance for 

 the understanding of the method of operation of the chromo- 

 somes In development. Their bearing will best be appreciated 



