172 



GENETICS IN RELATION TO AGRICULTURE 



tails from the color pattern of the Wild Rock Pigeon from the Shetland 

 Islands. 



The data which Darwin presented while giving qualitative evidence 

 of recombination of factors do not provide quantitative data on which to 

 base a Mendelian analysis. Staples-Browne, however, has presented 

 a case which admits of more definite analysis. He crossed a Black- 

 barb and a White Fantail and obtained black birds in F\. In F 2 he 

 obtained the results which are tabulated in Table XXXI. Cole has pro- 

 posed the following factor analysis for the principal colors in pigeons: 



B a factor epistatic to the series of factors which produce red in 

 pigeons, and giving black pigmentation. The allelomorph b then results 

 in red pigmentation. 



S a factor for extension of pigment which appears to act on B only. 

 BS gives black birds, whereas Bs gives birds in which the black pigment 

 is aggregated into clumps in the barbules, the so-called blue pigeons. 



T a factor which gives black tail feathers when B is present. The 

 allelomorph b under similar conditions gives blue tailed birds. 



W a series of factors for white pigmentation which Cole designates 

 Wi, Ws, W z , W n . By W n is designated simply an undetermined number 

 of these white factors which may affect different portions of the plumage. 

 Likewise by w n is designated the recessive allelomorphs of these white 

 factors, birds with such a genetic constitution being self-colored. 



TABLE XXXI. F 2 RESULTS FROM BLACK BARB X WHITE FANTAIL PIGEONS 



With these factors the Black Barb would be BBSSTTw n w n and the 

 White Fantail bbSSttWnW*. The Fi of such a cross, BbSSTtW n w n 

 would be black more or less splashed with white as were those obtained 

 in the experiment, and in F 2 , a series of forms would be obtained de- 



