POLYGAMOUS FACTORS 71 



other than black and red differ from each other abnor- 

 mally. Setting them out in the usual way, without 

 attributing to them either dominance or recessiveness, 

 the characters carried by black and the other four colours 

 should be : 



Black XYZA 



Red XYZa 



Light Dun XY zA 



Brown XyZA 



White xYZA 



and the last four colours should differ each from every 

 other in two pairs of characters. Yet we saw in the 

 last chapter that red and white differ from each other 

 in one pair only, and sufficient evidence has been col- 

 lected from the " Highland Cattle Herd Book " to show 

 that the other colours differ similarly in only one pair 

 of characters. Data with regard to the crossing of 

 white with light dun and brown have not been found, 

 but it is inconceivable that these crossings should not 

 be like the others. How are these phenomena, which 

 may be condensed into the statement that five inter- 

 mateable colours differ each from every other in only 

 one pair of characters, to be accounted for ? 



The problem may be simplified by considering only 

 three colours at a time, for what holds for three will 

 hold for the five. Black differs from red in one pair of 

 factors and from white also in one pair. Ordinarily, 

 without attributing dominance or recessiveness, the 

 colours and the characters they bear would be set out 

 as follows : 



Black XY 



Red Xy 



White X Y 



