230 GENERAL BIOLOGY 



gametes on the one hand, and, on the other, the 

 segregation of the unit characters in the zygote and 

 their 'chance union in subsequent zygoses. Subse- 

 quent investigation has shown that the problem is 

 by no means so simple as might be inferred from the 

 behavior of Mendel's peas. The " dominance " 

 of one unit-character over another has been shown 

 to be imperfect or non-existent in many cases, and, 

 more striking still, the character of the first hybrid 

 generation is not infrequently quite different from 

 either of the immediate parents. A remarkable 

 instance has been worked out in some breeds of 

 the domestic fowl. The following quotation from 

 Punnett's " Mendelism " gives the essential facts: 

 " Many of the different breeds of poultry are 

 characterized by a particular form of comb, and in 

 certain cases the inheritance of these has been care- 

 fully worked out. It was shown that the rose comb 

 (fig. 84, B}, with its flattened papillated upper sur- 

 face and backwardly projecting pike, was dominant 

 in the ordinary way to the deeply serrated high 

 single comb (fig. 84, (7) which is characteristic of 

 the Mediterranean races. Experiment also showed 

 that the pea comb (fig. 84, A), a form with a low 

 central and two well-developed lateral ridges, such as 

 is found in Indian game, behaves as a simple domi- 

 nant to the single comb. The interesting question 

 arose as to what would happen when the rose and 

 the pea, two forms each dominant to the same third 

 form, were mated together. It seemed reasonable 

 to suppose that things which were alternative to 



