270 



E. H. HARPER. 



potent color (B O) = subpotent sex -f prepotent color (G $). 

 For the prepotencies are nearly equal in this case (49.2:50.8). 



The figures for the 1,000 fillies are nearly the same as for 

 the colts (Table IV.). The black sires and gray dams are 

 in excess as before, there being 716 black sires to 284 grays 

 and correspondingly 716 gray dams to 284 blacks. The gray 

 dams are prepotent in 5 5 per cent, of the cases, black dams in 

 about 50 per cent.; gray sires in about 50 per cent., black sires 

 45 per cent. Here also the gray dams are more prepotent than 

 the gray sires (55:50). Also the relation holds as before ex- 

 pressed. B 9 = G $ (50.3:49.7). 



TABLE V. 

 PREPOTENCY IN RELATION TO COLOR. 



In Table V. are condensed the data of III. -IV. arranged with 

 reference to color alone. From this it is seen that gray parents 

 are prepotent in 54. 1 per cent, of the cases. Oddly enough this 

 almost coincides with the prepotency of dams (Table II.) which 

 was 54 per cent. This curious result comes from the fact pointed 

 out above that black dams mated with gray sires are almost equal 

 in prepotency in the case of both colts and fillies. Consequently 

 the whole difference between the prepotency of gray and black 

 parents arises from the unions between gray dams and black sires in 

 which the gray dams are prepotent in 55-56 per cent, of the cases. 



These results show from data independent of Table I. that 

 black is not a prepotent color. Therefore the secular change 

 shown in the increase of black in Table I. must be due to breeders' 

 selection. It is also evident that breeders' preference is exercised 

 by the more frequent use of black stallions. Although stallions 

 are chosen for their individual superiority and prepotency it would 

 seem that their superiority is not sufficient to make them pre- 

 potent as to color in the majority of cases. The original color 

 of the race, gray, is prepotent, having behind it the hereditary 

 force of previous generations of inbreeding. In the inheritance 

 of color the tendency is to return to the original gray. 



