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TEE AMERICAN NATURALIST [Vol. LVI 



ference between Dark Brahmas and Brown Leghorns, 

 the gene W" inhibiting the appearance of buff or red 

 in the hackles and saddles of Dark Brahmas. Jones 

 (1914) was probably dealing with a similar sex-linked 

 gene in his crosses between Silver and Golden Campines, 

 and Hagedoom's (1914) evidence indicates that the same 

 or a similar sex-linked gene differentiates Silver and 

 Grolden Assendelvers. Pnnnett (1919) distinguishes a 

 sex-linked gene S," which in crosses of Silver and 

 Golden Campines inhibited the development of buff or 

 gold in the plumage, leaving certain portions of the 

 feather ' ' silver ' ' or white. Most recently evidence pre- 

 sented by Haldane (1921) indicates that black and white 

 barring such as characterizes the Barred Plymouth Eock 

 variety is differentiated from black and buff (or red or 

 gold) barring by the same gene " S " for the inhibition 

 of buff. This sex-linked gene S," Haldane found to 

 be linked, as was to be expected, with the sex-linked gene 

 B " (barring). 



In each of these cases a dominant sex-linked gene was 

 found which restricted or inhibited the development of 

 buff (or red or gold) in certain parts of the plumage. 

 Although in the absence of data on crosses between the 

 varieties mentioned it is impossible to assert that the 

 restriction of buff in the silver or white-patterned vari- 

 eties is in each case due to the same gene, the presumptive 

 evidence in favor of such a view is strong. It appears 

 probable that Columbian and buff varieties of several 

 breeds (Leghorns, Plymouth Rocks, Wyandottes, etc.) 

 are differentiated by the presence in the Columbians of 

 a gene for the inhibition or restriction of buff pigment; 

 and in view of the history of the various color varieties 

 that this gene has been introduced into and now differ- 

 entiates Golden from Silver-laced Wyandottes, Golden 

 from Silver Spangled Hamburgs, gold pencilled (or part- 

 ridge) varieties from silver-pencilled ones and other 

 golden varieties from silver varieties which differ only 

 in the distinction between buff and white in the plumage. 



