J. A. S. Watson 65 



According to this the dun F^ females 2 and 5 would be BL and the 

 Fi male of course BR. The chances of the various combinations wf»uld be 



/ BB Black (homozygous) 

 I BR Black (heterozygous) 



1 BL Dun 



/ RL Yellow 



We should therefore expect a ratio of 



2 Black : 1 Dun : 1 Yellow. 

 The obtained results : 



2 Black : 5 Dun : 2 Red, 



not only suggest a different ratio, but give a colour which is not pro- 

 vided for by the scheme. As has already been pointed out by Babcock 

 and Clausen (14), Lloyd Jones and Evvard in the experiment, already 

 alluded to, obtained 6 reds out of 26 Fo in crosses of White Shorthorn 

 and Galloway, which again are inexplicable on Wilson's theory. The 

 latter, in its present form, must therefore be regarded as inadequate. 



Wright (15), on the contrary, has proposed a system of ordinary unit 

 factors, only two of which would be concerned in the present case, viz. : 



E, black, its absence e giving red, and 



D, a dominant pigment dilution factor, in whose presence black is 

 modified to dun, and red to yellow. The nine possible factor combinations 

 give the following respective colours : 



dclEE Black, homozygous 



dclEe Black, heterozygous 



ddee Red 



DdEE Dun (homozygous for black factor) 



DdEe Dun (heterozygous for black factor) 



Ddee Yellow 



DDEE Cream dun (homozygous for black factor) 



DDee Cream (light dun) 



On this hypothesis the male F^ 1 would be ddEe, and both dun 

 females, F^ 2 and F-^ 5, DdEe\ The possible combinations and the 

 probable frequency would then be : 



1 No. 5 might conceivably have been DdEE, although the chances are slight, black 

 being a comparatively rare colour among Highland cattle. The fact that she produced a 

 red calf, however, shows definitely that she was heterozygous for the black factor. 

 Journ. of Gen. xi ** 



