TYPES OF MENDELIAN HEREDITY 



31 



to fall under this heading: yellow dominates green, 

 round dominates wrinkled, etc. 



Whether a character is completely dominant or not 

 appears to be a matter of no special significance. 

 In fact the failure of many characters to show complete 

 dominance raises a doubt as to whether there is such 



Fig. 16. — a, Long wing (wild type) of Drosophila; h, miniature wing. 

 (a and h are not drawn to scale.) 



a condition as complete dominance. Some cases ap- 

 proach so nearly to that condition that special tests 

 may be required to show that the hybrid is affected 

 by the recessive factor. For instance, in flies the 

 factor for white eyes seems to produce no effect 

 when white is bred to red. The Fi reds are indis- 

 tinguishable from pure reds. But by weakening the 

 red by adding recessive factors other than white, 

 the influence of white can be demonstrated, as Mor- 



