470 GENETICS IN RELATION TO AGRICULTURE 
served facts is in the relation of bay, black, and chestnut to one another. 
Wilson’s formulation does not account for the production of bay foals from 
matings of chestnut and black, although such matings produce a large 
proportion of bay foals, whereas the first formulation accounts for them 
very simply. Moreover the first analysis is more nearly in harmony with 
our knowledge of the inheritance of coat color in rodents, which is so 
well understood that there is no question of this kind as to factor relations. 
Wilson’s formulation, however, is of this service: it points out clearly 
how uncertain are analyses based on herd book records, and thereby at 
the same time indicates the need of actual experimental investigation. 
It would be a very simple matter to demonstrate experimentally which 
of these analyses accounts for the actual factor interrelations. 
We cannot refrain here from indicating some of the consequences in 
breeding practice of a formulation such as the one we have favored in 
this discussion. The really important feature of the analysis, of course, 
lies in the emphasis it gives to the definiteness of phenomena of coat color 
inheritance in the horse. In every case there is a definite reason why a 
horse should be of a certain color, and the reason is comparatively 
simple. Moreover, since the phenomena are so definitely predetermined, 
it is possible within certain limits to control them. 
To take a definite instance, the government has set itself the task at 
the Iowa station of creating a gray breed of draft horses. Since gray is 
dominant to all the common horse colors save roan, it is impossible to get 
gray from matings of other colors. Moreover, grays when mated to- 
gether produce gray, bay, brown, black, and chestnut foals, according 
to the particular gray genotypes which are involved. Grays of the 
genetic constitution HhBbGg mated inter se produce the entire series of 
colors in the ratio 
48 gray:9 bay and brown:3 black:4 chestnut. 
The bay, brown, black, and chestnut offspring of such matings, or 
any other for that matter, might be mated together ever so often, yet 
they would never produce gray foals, although themselves the offspring 
of gray horses. 
Accordingly the method which should be followed in establishing a 
gray breed of draft horses is not difficult to map out. An effort should be 
made to get homozygous gray horses for breeding stock. Such horses, 
of course, will be met with only in breeds in which there is no prejudice 
against gray, as for example in the Percheron breed; but, if it should be 
thought desirable to utilize some of the good qualities of other breeds in 
which gray is not a favored color that may be done at the sacrifice of 
uniformity of color in the first generations. Matings should, however, 
always be of gray to gray individuals, and all animals of other colorsshould 
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