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. Darbishire 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 



