242 



THE THEORY OF THE GENE 



expectation for the tetraploid male, 4a+2X-f-Y (that has 

 not yet been obtained), is that he will be like the normal 

 male, since the balance is the same in both. 



This evidence from triploids gives no specific informa- 

 tion as to the occurrence of genes for sex-determination. 

 If we think of the chromosomes only in terms of genes, it 

 follows that genes are involved, but the evidence does not 



SuperfemaJ 



Fig. 139. 



Supermale 



Supersedes of Drosophila. The superfemale has thre e- sets of auto- 

 somes and three X-chromosomes. The supermale has three sets of 

 autosomes and an X- and Y-chromosome. (After Bridges.) 



Twc — 



show what they are like. Even if genes are involved, we 

 cannot state whether there is one gene in the X that 

 stands for femaleness, or hundreds of such genes. Simi- 

 larly for the ordinary chromosomes — the evidence does 

 not tell us whether the genes for maleness, if there be 

 such, are in all the chromosomes or in only one pair. 



There are, however, two ways in which we may hope, 

 some day, to discover something about the genes that 

 influence sex. The X-chromosome may become frag- 

 mented in such a way as to reveal the location of the spe- 

 cial genes relating to sex, if there are such. The other 

 hope rests on the occurrence of a gene mutation. If other 



