HYBRIDIZATION IN FOWLS 201 



the offspring will be white and others white with black splashes, 

 the remainder being like the parents. It has been shown, 

 moreover, that the three kinds of chicken occur, on an average, in 

 definite proportions, a quarter being black, a half blue, and a 

 quarter white splashed with black. Here we have the familiar 

 Mendelian proportion 1:2:1, suggesting that the blue Andalusian 

 is really a hybrid, and that the so-called " wasters " are the parent 

 forms. It is easy to prove that this is the case, for if the two 

 kinds of waster are mated we invariably get the blue Andalusian 

 again. The old idea of the so-called practical breeder w r ould have 

 been to go on destroying the wasters and carefully selecting the 

 blues in order to maintain the " purity of the breed." We now 

 know, however, that there is no such thing as a pure blue Andalu- 

 sian breed ; the blue is really a hybrid, and you can get more blues 

 by mating the wasters than by breeding from the blues 

 themselves. This case is also interesting as affording an example 

 of a hybrid which differs in character from either of the parent 

 forms. 



If only a single pair of alternative characters or allelomorphs is 

 dealt with in the experiment the case is termed one of mono- 

 hybridism, and such cases yield the proportion 1:2:1 (or 

 apparently 1 : 3 in cases of dominance) amongst the offspring of 

 the hybrid, i.e. in the F 2 generation. It will frequently happen, 

 however, that the two varieties which are united in the formation 

 of the hybrid will differ from one another as regards more than 

 one pair of contrasted characters. We may illustrate this by a 

 case of dihybridism, in which two pairs of contrasted characters 

 are involved. The case selected is one which shows us how, 

 under certain circumstances, we can obtain a hybrid exhibiting 

 an entirely new combination of characters, which in spite of its 

 hybrid nature will continue to breed true. 



Suppose a gardener had only two kinds of peas, one with round 

 green seeds and the other with wrinkled yellow seeds, and that he 

 wished to obtain peas with wrinkled green seeds. Mendel has 

 shown us how he may get what he desires, both surely and 

 speedily, from the material already in his possession. 



The necessary procedure will be evident from the following 

 scheme : 



Let R = round, W = wrinkled, Y = yellow, and G = green. 

 We know from previous experiments that R is dominant to W, 

 and Y to G. 



