ON THE INHERITANCE OF COLOR IN THE 

 AMERICAN HARNESS HORSE. 



A. H. STURTEVANT, JR. 



In a study of the English thoroughbred horse C. C. Hurst 1 has 

 shown that chestnut is recessive to bay and brown. He supposes 

 that the presence of black in the coat is the dominant character. 

 Now black, gray and most roan horses also have black in their 

 coats, but 95 per cent, of the English thoroughbreds are bay, 

 brown or chestnut, so that Hurst was unable to verify his supposi- 

 tion. The American trotting and pacing horse, however, a close 

 relative of the English thoroughbred, exhibits colors in proportions 

 much more favorable for an investigation of this kind. These 

 proportions are about as follows: bay, 53 per cent.; black, 

 13 percent.; brown, 15 percent.; chestnut, 14 per cent.; gray, 

 3 per cent.; roan, 2 per cent.; dun, .1 per cent. 



Perhaps before going further it will be well to give a brief dis- 

 cussion of these colors. According to Miss F. M. Durham, as 

 quoted by \V. Bateson, 2 there are three pigments, yellow, black 

 and chocolate, concerned in the color of horses, as in mice, rabbits 

 and other animals. Chestnuts have the yellow pigment alone. 3 

 Bays have both yellow and black pigments, and browns are only 

 very dark bays, shading into the self-colored blacks on the 

 other extreme. Grays have black hairs mixed with white ones, 

 usually in a dapple pattern. Roans are of at least three types. 

 The most common are the bay, red or strawberry roans, which 

 have yellow-black hairs* intimately mixed with white ones. 

 The black, blue or gray roans appear to differ from grays chiefly in 

 that their black and white hairs are more intimately mixed. The 

 chestnut roans have yellow and white hairs. As will appear later 

 the fact that there is no black in this class introduces a possible 

 source of error into my calculations. However, these chr-iiiut 



l Proc. Royal Soc., Vol. 77. B., 1906, p. 388. 

 "Mendel's Principles of Heredity," p. 125. 



'According to Bateson some chestnuts are really chocolates, but these an 

 the yellows in having no black. 



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