472 GENETICS IN RELATION TO AGRICULTURE 
shades, but on the whole our knowledge of the relations of the different 
shades to one another is very imperfect. In Shorthorn cattle red appears 
to breed true, at least records of white calves from red & red matings are 
so rare as to lead one to suspect they were due to error of registration. 
Compared with white in this breed red represents a condition of extended 
pigmentation, dependent upon the dominant factor, FE. Here a difficulty 
is introduced by the fact that red X white matings ordinarily produce 
roan rather than red and white offspring. 
Fig. 188.—A white polled heifer with black ears and muzzle; an F2 individual from the 
cross Galloway X white Shorthorn. (After Lloyd-Jones and Evvard.) 
The roan color in cattle, like roan in horses, appears to depend upon a 
definite dominant factor, R. Strictly of course roan is not a color, but a 
pattern effect due to admixture of white hairs in a pigmented coat, and it 
may affect black as wellas red. This roan type of coloration is character- 
istic of Shorthorn cattle. The predominance of roan animals in this breed 
probably accounts for the fact that white mated to red usually gives roan 
offspring, for the whites are derived almost wholly from roan matings 
and they should therefore of necessity often bear the roan factor. There 
are also some apparently authentic accounts of red and white animals, 
the progeny of matings of red X white, such as the case of the noted white 
Shorthorn bull, Whitehall Sultan, which sired fifteen red calves out of 
various red cows. Were it not for this, J. Wilson’s assumption that roan 
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