Black♂ Barred♀ P₁ ZᵇZᵇ ZᴮW \ / \ / \ / ZᴮZᵇ ZᵇW F₁ Barred♂ Black♀ \ / \/ ZᴮZᵇ ZᵇZᵇ ZᴮW ZᵇW Barred♂ Black♂ Barred♀ Black♀
One back-cross test consists in mating the F₁ barred males ZᴮZᵇ (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 F₁ barred hen of the first cross (ZᴮW) 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:
Black♂ F₁ Barred ♀ ZᵇZᵇ ZᴮW \ / \/ ZᴮZᵇ ZᵇW Barred♂ Black♀
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 reciprocal 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 allelomorph 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 expectation. The results were the same as those already stated above for the Langshan-Rock cross.