120 POULTRY CULTTXRE 



possessed by the Single Comb White Leghorn, and it has also 

 been shown that the pea comb is dominant to the single comb. 



Thus we see two dominants in the rose and pea combs. 

 When a rose comb is crossed on a pea comb a new type is 

 formed, that of the walnut comb (so-called because it resembles 

 half of a walnut) . 



According to Fig. 42, we will see that the F2 generation, that 

 is, the progeny of the rose comb and pea comb crossed on each 

 other, produced foiu- types of combs, as follows: 9 walnut, 3 

 rose, 3 pea, and 1 single. According to Punnett, these are 

 always produced in this proportion. 



In the analysis of the above we conclude that the walnut 

 comb contains both dominant characters, the pea comb and 

 rose comb one dominant each, and the single comb as a pxire 

 for both recessive characters. 



The pea comb and rose comb factors are distinct and sepa- 

 rate entities which, when combined, have an influence on each 

 other in the zygote, producing the walnut comb which is not 

 an intermediate between the two. 



When one of these factors are alone in the zygote its influence 

 in the single comb factor is different; that is, producing a pea 

 comb if a pea comb factor or a rose comb if a rose comb factor. 



The single comb is the form found in the wild jungle fowl, the 

 Bankiva, which is said to be the ancestor of all our domes- 

 tic fowl. If this be true the reversion to the single comb in 

 the F2 generation is easily explained. It is a reversion pure 

 and simple, the recessive factor coming to the surface. This 

 is considered as due to the association of two complimentary 

 absences. 



Punnett found that by crossing a White Dorking on a White 

 Silky fowl, both of which had been shown to behave as simple 

 recessives to color, the Fi generation consisted of colored birds; 

 the F2 generation consisted of colored and white, in the ratio 

 of nine to seven. This is, in reahty, the 9:3:3:1 ratio as ob- 

 served in a study of the crossing of comb characters. The 

 3:3:1 factors are indistinguishable because they cannot pro- 

 duce visible effects without the co-operation of each of these 

 section factors. 



Another excellent illustration is shown in the breeding of 



