THE NATURE OF GENES 181 



which developed from the egg. In that case the chromosome 

 change might be regarded as a gene responsible for the ob- 

 served departure from normality. As such it would behave 

 in crosses with normal individuals. If this is true, it seems 

 probable that the entire chromatin, or at least so much of 

 it as is concerned in determining the activities of the cell, 

 may be regarded as composed of genes. A gene will be the 

 smallest part of the chromatin capable of varying by itself. 

 And if the gamete contains any structures not chromatin 

 which are concerned in heredity, that is which are repro- 

 duced when the cell divides, these too will constitute genes. 

 Further investigation alone can show whether or not genes 

 are found exclusively in the chromatin. At present it is 

 assumed that such is the case. 



