INHERITANCE IN ORGANISMS 



563 



one white recessive. Another case of incomplete dominance is that 

 of the blue Andalusian fowl (Fig. 387), which is a hybrid between a black 

 individual and an individual which is white splashed with black. When 

 two blue Andalusians are bred, there is a ratio of one splashed white, one 

 black, and two blue individuals. 



Another variation is that due to the cumulative effect of multiple 

 genes. This is observed in mulattoes, whose skin color may vary from 

 very dark to very light. It also has been found that there are lethal 



P Gen 



F2 Gen. 



Fig. 387. — Incomplete dominance, as illustrated by the blue Andalusian fowl. The 

 P generation is splashed white and black, the Fi generation all blue, and the F2 generation, 

 one splashed white, two blue, and one black. 



genes, which when present in pairs cause the death of the organism. In 

 some cases, as walnut combs in fowl, the character is believed to result 

 from the interaction of two genes, either kind of which, when in a homo- 

 zygous pair, produces a different comb pattern. 



606. Breeding for Certain Characteristics. — In both animal and plant 

 breeding the end sought is the bringing together of desirable characters 

 and the development of stock which will breed true for those characters. 

 This involves the careful selection of breeding animals and the elimina- 

 tion of all progeny which are not homozygous for each pair of characters 

 desired. In this way, and by persistent inbreeding, a line can gradually 

 be developed which not only possesses the desired characters but also 



