28 THE GENETIC AND THE OPERATIVE EVIDENCE 



One back-cross test consists in mating the F! barred males Z B Z b 

 (from both crosses) to a pure black female. The expectation is for 

 equal numbers of barred and black males and females, and the result 

 was realized. The FI barred hen of the first cross (Z B W) back-crossed 

 to a black cock is expected to give only barred males and black females, 

 and this result also was obtained. The explanation of the last cross, 

 based on the sex chromosomes, is as follows : 



Barredj 



Barred c? 



Before these experiments were finished Goodale had made other 

 crosses involving the barring factor, and had obtained results that 

 showed the sex-linked inheritance of this factor (1909). For example, 

 he crossed Buff Rock male (not barred) to white Plymouth Rock 

 females. The sons were barred and the daughters not barred. The re- 

 ciprocal cross gave barred sons and daughters. A White Rock male 

 (carrying barring) mated to a Brown Leghorn female gave barred sons 

 and daughters. Reciprocally, the chicks were of two kinds as to their 

 down, viz, black chicks and chicks with the down pattern of the barred 

 rock. All these results with Barred Plymouth Rocks show that they 

 carry a sex-linked dominant factor for barring. Its wild-type allelo- 

 morph would be game-color (jungle-fowl), but since, when the dominant 

 barring is absent in some of the individuals in these crosses, they are 

 black, it would seem to follow that another dominant factor, one for 

 black, that is not sex-linked, is also present. 



Pearl and Surface have also carried out crosses with Plymouth 

 Rocks on a much larger scale. Their results conformed in every way 

 to the foregoing. They crossed Barred Plymouth Rocks and Cornish 

 Indian games. The plumage of the male of the latter race is black 

 with dark red on the back and wing-bows; the females are also black 

 laced with mahogany ground-color on back, breast, wing, and tail 

 coverts. When the male game is mated to the barred hen the sons are 

 barred and the daughters are black. In the reciprocal cross both sons 

 and daughters are barred. The back-cross tests conformed to expecta- 

 tion. The results were the same as those already stated above for the 

 Langshan-Rock cross. 



Sturtevant crossed Columbian Wyandottes and Brown Leghorns. 

 The F! sons were alike, whichever way the cross was made. They were 

 fairly typical Wyandottes, which race carries therefore more of the 

 dominant plumage characters (two or three?). There were two types 

 of daughters, depending on the direction in which the cross was made. 



