INCOMPLETE DOMINANCE 319 



All the young chicks were a queer mixture of mottled black and 

 white which is known as blue. They were mixtures and not pure 

 bred like their parents. When the members of a pair of widely 

 different unit characters, in this example, black and white feathers, 

 meet in an offspring, the offspring is called a hybrid. Evidently, 

 neither the black nor the white character could mask or dominate 

 the other, and a blending took place. The blending of a pair of 

 characters is called incomplete dominance. 



Next, the investigators wished to discover what the descendants 

 of the hybrids would be like. Only blue Andalusian fowls, hybrids, 

 were chosen for this part of the experiment. This hybrid gener- 

 ation is known as the FI generation or the first filial generation. It 

 was found that the offspring of hybrids varied in color. Some were 

 blue like their parents, some were white like one grandparent and 

 some were black like the other grandparent. When a large number 

 of them were examined, it was found that the different colors of 

 the chicks always occurred in the same proportion. For every two 

 chickens that were blue like their parents, there was one black 

 and one white chicken. In other words, 25 per cent were black, 

 25 per cent were white, and 50 per cent were blue. This genera- 

 tion, in which there was a reversal to ancestral type by the segre- 

 gation of the original unit characters, is known as the second filial 

 or the F 2 generation. Evidently, the original characters must have 

 retained their identity since some of the offspring showed one char- 

 acter and others showed the opposite character. 



The next step in the experiment was to find what would happen 

 when the different members of this mixed group became parents. 

 A black fowl was mated with another black and all the offspring 

 were black. In other words, the black chickens of the F 2 gener- 

 ation not only looked black like their black grandparents, but were 

 pure as shown by the fact that they had only black descendants. 

 They possessed only genes or character-determiners for black. 



A white of the F 2 generation was mated with another white and 



