66 Mendelian Experiment with Cattle 



1 DdEE (dun), 2 BdEe (dun) = 3 dun 

 1 Bdee (yellow) = 1 yellow 



1 ddEE (black), 2 ddEe (black) = 3 black 

 1 ddee (red) = 1 red. 



The results obtained, 5 dun, 2 black, 2 red, while not agreeing closely 

 with expectation, contain nothing that is definitely opposed to Wright's 

 hypothesis. 



It is obvious, however, that, so far as concerns the present experiment, 

 a third explanation is possible, which has the merit of greater simplicity, 

 viz. that the factor D is not a colour dilution factor, modifying both 

 black and red, but an independent factor for dun colour, epistatic to E 

 (black), and producing dun whenever present. This hypothesis would 

 give an expected ratio of 4 dun, 3 black, 1 red, which is comparatively 

 near to the ratio obtained. The numbers are, however, obviously too 

 small to furnish any definite proof of such an hypothesis. 



Conclusions. 



(1) The polled and horned conditions form a simple Mendelian pair. 

 The polled condition is completely dominant in the female, while in the 

 heterozygous male horn development is inhibited but not always sup- 

 pressed. 



(2) Black is dominant to red, and the colours behave as a simple 

 Mendelian pair. 



(3) The hypothesis of multiple allelomorphs for colour, proposed by 

 Wilson, is not in agreement with the results obtained. 



(4) Dun is dominant to black, but whether as a simple epistatic, or 

 whether produced by a dilution factor capable of modifying colours 

 other than black, does not appear from this experiment. 



The author desires to express his thanks to the Moray Fund for 

 Research, Edinburgh University, and to the Board of Agriculture for 

 Scotland, for the necessary funds; to Lord Forteviot of Dupplin for 

 providing facilities for the woi'k, and to his lordship's agent, Mr J. J. 

 Simpson ; to Mr Wm. Bruce, B.Sc, Edinburgh and East of Scotland 

 College of Agriculture, who supervised the experiment during the greater 

 part of the period 1914-1918 ; and to Prof J. Cossar Ewart of Edinburgh 

 University, and Sir R. B. Greig of the Scottish Board, for assistance 

 and advice. 



