30 THE GENETIC AND THE OPERATIVE EVIDENCE 



prefixed the number of individuals. The cross also involved hen- 

 feathering versus cock-feathering, which appears here (as in other 

 cases) to be a non-sex-linked dominant factor. As stated above there 

 are in the results a few apparent inconsistencies with this interpre- 

 tation, due possibly to heterozygous females having been used in the 

 crosses. 



Lefevre crossed Silver Spangled Hamburgs and Brown Leghorns. 

 The spangling was found to be a sex-linked dominant factor. A span- 

 gled cock bred to a Leghorn hen gives spangled sons and daughters; a 

 spangled hen by a Leghorn male gave spangled sons and not spangled 

 daughters. The daughters do not transmit spangling. Other factors 

 may obscure the results, especially factors for black, or the localization 

 of the pattern. Lefevre says "it would seem probable that multiple 

 factors for black, introduced by the Brown Leghorns, are present, and 

 that these factors may have a cumulative effect, with the result that 

 pigmentation is developed to varying degrees of extension." Whether 

 the factors for black spoken of as coming from the Leghorns are 

 dominant wild-type factors that have mutant allelomorphs in the Silver 

 Spangled Hamburg is not entirely clear from the quotation. 



Baur gives in his Introduction to the Study of Heredity (1914, 

 pp. 202-203) some results (unpublished) that Hagedoorn had obtained 

 by crossing gold and silver races of Assendelver birds. The factor 

 is sex-linked and is no doubt the same factor reported by Jones for 

 gold and silver Campines and by Sturtevant for Columbian Wyan- 

 dottes. Silver dominates gold and the sex relations are the same as 

 those already reported by others for poultry, viz, the male is ZZ, the 

 female ZW. Gold hens by a heterozygous silver 1 gave 162 silver cocks, 

 163 silver hens, 168 gold cocks, 160 gold hens, expressed graphically 

 (g for gold, s for silver) : 



Z g -W9XZ — Z^cT 

 Z*Z»— Z"Z"— Z 3 W— z»w 



Silver Gold Silver Gold 

 male male female female 



When a silver hen was united to a gold cock there were 246 silver 

 cocks and 243 gold hens — crisscross inheritance. 



Summary. 



From the standpoint of the Brown Leghorn type representing the 

 wild type, the following colors and patterns represent dominant 

 mutations from that type: 



Dominants. 

 White of White Leghorn. Barring of Plymouth Rock. 



Silver of Dark Brahma. Black (?) of Plymouth Rock. 



Black of Minorca. Buff (or red). 



Lacing of Brahma. 



1 No mention is made by Baur that a heterozygous male instead of a pure silver male was used, 

 although the male is made heterozygous in the formulae. 



