GENES AND CHARACTERS 



321 



Fig. 185. — The factor hypothesis applied to colors of rabbits. (From Walter.) 



Explanation: Br=a gene acting on C to produce brown pigmentation. 



B = a gene acting on C to produce black pigmentation. 



Y = a gene acting on C to produce yellow pigmentation. The three genes, Y, B, Br, are present 

 in every rabbit gamete and up to date have not been separable as independent unit 

 characters, although they have been separated out in guinea-pigs and mice. There are 

 no brown rabbits, because black always goes linked with brown, covering the brown 

 factor. Yellow rabbits result, as explained below, through the action of factor e. 



C = a common color gene necessary for the production of any pigment. It was discovered in 



190.3 by Cu^not. 

 c=the absence of C which results in albinos, regardless of whatever pigment gene may be 

 present. By changing C to c, sixteen kinds of albinos would be added to this catalogue, 

 an addition of one phenotype and sixteen genotypes, all looking alike but breeding 

 differently. 



E = a gene governing the extension of black and brown pigment, bid not of yellow. 

 e=the absence of extension or restriction of black and brown pigment to the eyes and the 

 skin of the extremities only, while yellow remains extended and visible. Demonstrated 

 by Castle in 1909. 

 I = an intensity gene which determines the degree of pigmentation. It can be transmitted 



independently of C through an albino. Discovered by Bateson and Durham in 1900. 

 i = the absence of intensity or dilution. Dilute black = blue. Dilute yellow = cream. Dilute 

 gray = blue-gray. 



U = a gene for uniformity of pigmentation or "self-color" discovered by Cu6not in 1904. 



u= the absence of uniformity which results in spotting with white. 



A = a pattern gene for agouti, or wild gray color, which causes the brown and black pigments 

 to be excluded from certain portions of each hair, resulting in the gray coat. When 

 present in the rabbit it is also associated with white or lighter color on the under sur- 

 faces of the tail and belly. It was demonstrated by Castle in 1907. 

 a = the absence of the agouti or pattern gene. 



