RELATION OF GENES TO CHARACTERISTICS 1 87 



purple; the modified gene giving this color Is known as pur- 

 ple. But In other cases what Is outwardly the same color is 

 found to be produced by change In other genes. One of these 

 Is at I, 44.4; to distinguish It from the one just mentioned 

 It is called garnet. A third gene that produces practically the 

 same eye color Is found at III, 49.7 ; It is called maroon. 



Similarly the eye color "salmon," resulting from a mod- 

 ified gene In I (again at 44.4), is Indistinguishable from the 

 eye color "rose," resulting from a gene modification at III, 

 48.0. 



Other cases of this sort could be given. In such cases the 

 same phaenotypic character will be found to be Inherited In 

 different ways In different cases, depending on the location 

 of the modified gene to which the character Is due. If the 

 gene Is In X, the Inheritance will show itself to be of the 

 sex-linked type; If in II, It will be autosomal and of the 

 linkage Group II; if In III It will be autosomal and of the 

 linkage Group III (see Chapter IX, on Rules and Ratios of 

 Inheritance). 



The Action of Genes in Development 



In view of what has just been set forth, how are we to 

 conceive the operation of the genes in producing the char- 

 acteristics? How do they operate In producing an adult 

 from the fertilized egg? And how do different sets of genes 

 produce Individuals having different characteristics? 



On the Intimate details of the operation of the genes little 

 Is known. Some of the main features in their method of 

 action were taken up In Chapter III, In dealing with the 

 relation of chromosomes to sex, though only the action of 

 large groups, forming chromosomes, was there dealt with. 

 From the relations brought out above, and In preceding 

 chapters, taken In connection with the facts of embryological 



