MENDELISM 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 cci7(BZ)(BZ); male, or ccii(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 F, birds, all of which were white, although some of 
them showed a few barred or black-flecked feathers. This is shown in 
the F, bird in Fig. 191. Mating such F, birds together should give in F, 
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. 
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