BLENDING INHERITANCE 177 



produce red, roan, and white offspring in the propor- 

 tion of 1:2:1, thus showing that roan is a heterozy- 

 gous character in which the dominance of red is 

 imperfect. 



Even in cases of apparently perfect dominance it 

 is sometimes possible by close inspection to detect 

 differences between a pure dominant {DD), Figure 43, 

 and a heterozygous dominant [DR] when a superficial 

 examination is not sufficient to distinguish them. 



For instance, in the cross between smooth and 

 wrinkled peas, a microscopic examination of the 

 starch-grains in the cotyledons of the hybrid peas 

 shows that they are of two kinds. Darbyshire calls 

 attention to the fact that, in the power of absorption, 

 hybrid smooth peas {DR) are intermediate between 

 their pure dominant smooth {DD) and pure recessive 

 wrinkled {RR) parents. 



3. Delayed Dominance 



A character which is really dominant is sometimes 

 so late in manifesting itself in the individual growth 

 of the offspring that it may properly be termed a 

 delayed dominant. 



Dark-haired individuals often do not acquire their 

 definitive hair color until adult life, and it is common 

 knowledge that the eyes of an infant for a consider- 

 able period provoke no little speculation among ador- 

 ing relatives as to " whose eyes " they are. 



According to Davenport, when a white Leghorn 

 fowl is crossed with a black Leghorn, white being 

 dominant in this case, chicks are produced that are 



N 



