488 



The Joi'RXAL of Hkreditv 



appears to work independent of the 

 determiners for the colors. 



There is a reason in the behavior of 

 color factors, in transmission, why a 

 coming foal shall be a bay. Actinj:; in 

 the same yjerm cells for this foal is the 

 factor for the roan condition and the 

 combined result of the two factors is to 

 produce a bay roan. Should the factors 

 for color have been black or chestnut in- 

 stead of bay the roan factor would have 

 acted in the same manner except the 

 result on the foal would ha\-e been a 

 black roan or a chestnut roan, accordinj^ 

 to the resultant of the factors for tliose 

 colors. 



The determiner for roan is present or 

 not present in the germ plasm. If 

 present it will be seen in the coat of the 

 mature horse. Its jjresence is dominant 

 over its absence. It in no way interferes 

 with the inheritance of the colors among 

 themselves. 



Like the gray, roan cannot always be 

 detected in young foals. They appear 

 to be bay or black at first, and some 

 show this condition until they shed, 

 when the roan becomes visible. 



When once in the germ plasm of a 

 strain of horses its persistence is re- 

 markable. The famous trotting sire 

 Ja\' Bird got his roan from his grand- 

 mother, Lady Franklin, about whose 

 ancestry we know nothing. A large 



percent, of the get of Jay Bird were 

 roan and it lingers in his descendants to 

 some extent even to the present. But 

 when it disai)ijcars it is like the gray, it 

 will not reapjjcar. To get it again it is 

 necessary to go back to it. 



A good illustration came to our 

 attention recenth'. An intelligent 

 horse breeder bred the progeny of a 

 famous gray horse for five or six genera- 

 tions. He lost the gray at the begin- 

 ning, but did his breeding exjjecting it 

 to reappear mth each new generation. 

 He of course met mth disa])])ointment.^ 



So alike is the behavior of gray and 

 roan that the e\ndence points to a unity 

 of the two. The gray horse is, perhaps, 

 one form of the black roan. When the 

 pattern is in the dappled form which 

 with the black disaj^j^ears \\ith age, we 

 call it gray. The difference between 

 the gray and black roan is only one of 

 l^attern and the quantity of white hairs. 

 The white is much more plentiful in the 

 gray than in the roan. It is a question 

 of quantity, I believe, and not of kind 

 which distinguishes the roan from the 

 gray. I am confident that further 

 research will show a close relationshi]) 

 of the factors for gray and roan. 



There is evidence that dun is domi- 

 nant to the solid colors, but there is no 

 evidence of the comparative strength 

 of gray, roan and dun. 



* By eliminating at each generation the few chestnuts produced, a breeder can easily secure a 

 family of horses that will produce notlvng but blacks. To produce a family of bays requires more 

 time and i)a(ience, since the external appearance of a bay tells us little of his genetic qualities. 

 Grays are becoming scarce and of very mixed ancestry — to produce a family of horses that bred 

 pure gray would now be a difficult task for any except the Percheron breeder. 



BIBLIOGRAPHY. 



Proceedings Royal Society 77 B, 

 in Horses. 



Hurst, C. C. — On the Inheritance of Coal Color In Horses 



1906. 

 Sturtev.\nt, a. H. — A Critical Examination of Recent Studies on Color Inheritanc 



Journal of Genetics, February, 1912. 

 Haki'KR, E. H.— Biological Bulletin, October, 1913. 



Wilson, Jamks. — Scientific Proceedings of llie Royal Dublin Society, No. 28, 1910. 

 VVkntworth, E. N. — Color Inheritance in the Horse. Sonderabdruck aus der Zeitschrift fiir 



induktive Abstammungs und Vererbungslehre, 1913, Bd. 1 1, Heft 1 u. 2. Verlag von Gebriider 



Borntraeger in Berlin VV. 35. 

 Anderson, W. S. — The Inheritance of Coat Color in Horses. American Naturalist, October, 



1913. 



