170 GENETICS 



been obtained by Castle and other experimental 

 breeders as well as many of the albino types that 

 would double this list if c, or the factor for absence of 

 color, should be substituted for C, the presence of 

 color, in column 4 of the table on page 169. 



Explanation of Symbols in the Foregoing Table 



Br = a factor acting on C to produce brown pigmentation. 



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



F = a factor acting on C to produce yellow pigmentation. 

 The three factors, F, B, Br, are present in every 

 rabbit gamete and up to date have not been sepa- 

 rable 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 factor necessary for the production 

 of any pigment. It was discovered in 1903 by 

 Cuenot. 



c = the absence of C which results in albinos, regardless 

 of whatever pigment factors 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 factor governing the extension of black and brown 



pigment, but 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. 



