MEN DELI SM IN DOMESTIC ANIMALS 479 



C a factor for black coloration. The allelomorph, c, determines the 

 production of recessive white plumage. 



I a dominant factor for white pigmentation, which supresses the 

 normal production of pigment in the plumage. 



B the sex-linked dominant factor for barring, a pattern factor, 

 which acts on black to produce the familiar plumage effect of the Barred 

 Plymouth Rock. The recessive, bb, birds are solid color. 



Z the sex-factor, homozygous in males, and mated to the neutral W 

 in females. Hadley found that the White Plymouth Rock was probably 

 of the genetic constitution ccii(BZ)(BZ); male, or cdi(BZ)W, female; 

 and obtained results which accorded with this formulation. From 

 matings of White Plymouth Rock females and White Leghorn males, 

 Hadley obtained 63 FI birds, all of which were white, although some of 

 them showed a few barred or black-flecked feathers. This is shown in 

 the FI bird in Fig. 191. Mating such FI birds together should give in F 2 

 white and barred birds in the ratio of 13 white :3 barred. The actual 

 figures obtained were 134 white :33 barred, a very close agreement with 

 expected results. Facts such as these demonstrate with what care the 

 breeder must proceed in crossing breeds if he wishes to avoid obtaining 

 a heterogeneous mixture of classes in subsequent generations. 



