COLOR INHERITANCE IN MAMMALS 



IV. The Rabbit— Has Three Sets of Multiple Allelomorphs Which, as in Six Other 



Cases in Mammals, Determine Linear Series of Physiological Effects Not 



to be Explained as Mere Linkage of Factors in the Germ-cells 



Sewall Wright 

 Bureau of Animal Industry, Washington, D. C. 



RABBITS are very rich in color 

 varieties and more unit differ- 

 ences from the wild gray have 

 been thoroughly demonstrated 

 than in any other mammal. The ten 

 known unit differences listed in the box 

 below fall into seven independent sets of 

 allelomorphs. In three cases triple 

 allelomorphs have been proved. Most 

 of the possible combinations of these 

 factors have been made but partial 

 coupling does not seem to have been 

 thoroughly investigated. 



The two white patterns — English and 

 Dutch — make an interesting compar- 

 ison. Hurst "^ showed that the Dutch 

 pattern is due to a unit factor which is 

 nearly recessive. Heterozygotes gener- 

 ally show a small amount of white. 

 There are all variations in the pattern 

 from a very little white to black-eyed 

 white, but the mode of inheritance of 



Wild Gray Rabbit— w S 1 C A E B {Pat- 

 tern of black and yellow) 



lai W,w W — English pattern 



la2 S,s s — Dutch pattern 



las I,i d — dilute gray (blue and 



cream) 

 lb C, Ch, Ca Ch — Himalayan, Ca — 



albino 

 2ai A, At, Ab At — black and tan, Ab — 



black 



2a2 

 2a3 

 2b 



Ed, E, Ey Ed— black, Ey— yellow 

 B,b b — ^brown agouti (brown 



and yellow) 



Classification explained in paper on the 

 mouse, Journal of Heredity, 8:373, 

 August, 1917. 



these differences has not yet been 

 solved. Hurst^ found the English pat- 

 tern to be dominant on the whole, 

 although the heterozygote shows dis- 

 tinctly more color than the homozygous 

 English. These results have been con- 

 firmed by all later work. 



The fundamentally different biochem- 

 ical nature of the two patterns was 

 shown by Onslow as discussed in the 

 first paper of this series. He found an 

 enzyme inhibitor in the skins of English 

 rabbits but merely an absence of the 

 enzyme, tyrosinase, in Dutch rabbits. 

 There is considerable difference in 

 appearance. As in other piebald mam- 

 mals, the Dutch rabbit has large colored 

 areas with solid boundaries sharply 

 separated from the white parts. In the 

 English pattern, there is a greater 

 breaking up of the spots and at the 

 borders white and colored hairs are 

 intermingled. This pattern holds a 

 somewhat isolated position at present. 

 It can hardly be compared with the 

 so-called dominant white of mice which 

 seems to belong to the piebald class. 

 It is perhaps most closely allied with the 

 dominant whites among the larger 

 animals as in the white of Shorthorn 

 cattle or of sheep. In these, however, 

 there is a tendency toward a uniform 

 roan in the heterozygotes. On this 

 basis, the English factor is put in class 

 lai, while the Dutch factor is put in 

 class la2. 



The maltese type of dilution is familiar 

 in rabbits and was found by Castle^ to 

 be a Mendelian recessive. This factor 

 reduces yellow to cream as well as 

 black to blue. It resembles closely 



1 Hurst, C. C. 1905. Linn. Soc. Jour. ZooL, 29:283-324. 



2 Hurst, C. C. 1906. R. Hort. Soc. London, p. 114. 



3 Castle, W. E., Walter, H. E., MuUenix, R. C. and Cobb, S. 

 Pub. No. 114. 68 pp. 



1909. Cam. Inst. Wash. 



473 



