PHENOMENA OF INHERITANCE 273 



pletely dominant over white, while the reds 

 and whites are homozygotes and consequently 

 breed true. 



Lang found that when snails with uniformly 

 colored shells were crossed with snails having 

 bands of color on the shells the hybrids were 

 faintly banded, thus being more or less inter- 

 mediate between the two parents; but when 

 these hybrids were interbred they produced 

 banded, faintly banded and uniformly colored 

 snails in the ratio of 1:2:1, thus proving that 

 Mendelian segregation takes place in the F 2 

 generation, and that dominance is incomplete 

 in the heterozygotes. Many other similar 

 cases of incomplete dominance are known. 



Sometimes dominance is incomplete in early 

 stages of development but becomes complete 

 in adult stages. Davenport found that when 

 pure white and pure black Leghorn fowls are 

 crossed the chicks are speckled white and 

 black, but in the adult fowl dominance is com- 

 plete and the plumage is black. Similar con- 

 ditions of delayed dominance are well known 

 in the color of the hair and eyes of children, 

 though dominance may become complete when 

 they have reached adult life. 



