Hadley: The White Leghorn 



149 



makes its appearance in F2? It cannot 

 have come from the Black Hamburg 

 grandparent since we know that in 

 every case where the factor for barring 

 is added to black pigmentation, the 

 barred pattern is^ brought out. It 

 must therefore have come from the 

 White Leghorn. In other words, the 

 White Leghorn itself carries factors for 

 this barred pliimage pattern. 



BREEDING BLACK FROM WHITE. 



But this is not all. If a White Leg- 

 horn male be mated with a White 

 Plymouth Rock or a White Silky 

 female or with any other bird carrying 

 recessive white, the first generation 

 progeny are white, sometimes mani- 

 festing on close inspection a few black- 

 flecks in the plumage. No colored 

 birds result. Now suppose these F, 

 white fowls are mated together. One 

 would naturally expect nothing but 

 whites to result. But this is not the 

 case. Among every sixty-four adult 

 individuals, there appear approximately 

 twelve birds that are dark colored 

 — either barred or black, depending 

 upon the cross used. It may now 

 be asked whence came the black 

 birds in a cross in which the original 

 parents were pure white? In the 

 case of the White Plymouth Rock 

 mating, we know that the White Ply- 

 mouth Rock parent could not have 

 introduced the black because, whenever 

 a black factor is added to a recessive 

 white carrying the barring factor, the 

 pattern becomes patent and the bird 

 becomes a Barred Rock or "Cuckoo." 

 We are therefore forced to one of two 

 conclusions: (1) Either the White Leg- 

 horn parent contributed the black pig- 

 mentation or (2) the pigmentation was 

 produced by the conjunction of two 



factors of which the White Leghorn and 

 the White Plymouth Rock each contrib- 

 uted one. By Mendelian analysis of 

 the experimental results,, this question 

 can be answered. It results in this: If 

 one of these factors for black (X) comes 

 from the Leghorn, and the other (Y) 

 comes from the White Plymouth Rock, 

 then the number of dark colored birds 

 in Fo is nine in sixty-four. If on the 

 other hand, the White Leghorn intro- 

 duces all the factors necessary to deter- 

 mine black pigmentation in Fo progeny, 

 the number of dark colored birds would 

 be twelve in sixty-four. In the actual 

 experiments carried out at the Rhode 

 Island Agricultural Experiment Station, 

 among 167 F2 birds raised from the 

 mating in question, thirty-three were 

 dark colored and 134 were white. The 

 expectation was dark colored, 31.2; 

 white 135.8. It can therefore scarcely 

 be doubted that the White Leghorn 

 male carries in its germ cells all the 

 factors necessary for the determination 

 of black pigmentation in the F2 genera- 

 tion of crosses with non-pigmented 

 breeds. 



THE FACTS EXPLAINED. 



Now what is the explanation of these 

 phenomena? It has been stated that 

 the White Leghorn possesses a dominant 

 white. But white in the plumage of 

 poultry is merely the absence of color 

 and the absence of color can scarcely 

 be dominant over the presence of color. 

 It must be assimied therefore that the 

 Leghorn white is due to some positive 

 inhibiting factor (I) which in some way 

 is able to repress or to neutralize the 

 black pigment, not only in its own 

 somatic cells, which would otherwise 

 show black, but also in crosses with 

 other black breeds. When I is present 



THE WHITE LEGHORN UNMASKED. 



(See illustrations on opposite page.) 



Although the White Leghorn is considered a "pure breed," it is very far from being a pure breed, 

 from a genetic point of view. Its germ cells even contain a factor for barring, so that barred fowls 

 can be produced from certain matings of pure white fowls. Upper left is a White Leghorn male, 

 which v/as mated with a White Plymouth Rock female such as is shown in the lower left. From 

 this cross resulted birds like the one shown in the upper right— nearly solid white, but with occa- 

 sional black splashes. When these birds are bred together, a definite proportion (12 in 64) of the 

 offspring are barred, like the bird shown in the lower right. Further analytic breeding proves that 

 this barring is carried in the germ-plasm of the White Leghorn, not the White Plymouth Rock. 

 (Fig. L) 



