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 toshow complete ° 
dominance raises a doubt.as to whether there is such 
Fie. 16.—a, Long wing (wild type) of Drosophila; b, miniature wing. 
(a and b 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 F, 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- 
