THE BLACK-AND-TAN RABBIT AND THE SIG- 

 NIFICANCE OF MULTIPLE ALLELOMORPHS 



W. E. CASTLE AND H. D. FISH 

 Bussey Institution, Forest Hills, Mass. 



It is well known that the European rabbit has under- 

 gone great variation, and now exists in a large number of 

 domesticated varieties. Darwin and most other natural- 

 ists speak of this as " variation under domestication," 

 implying that domestication has caused the variation. 

 Modern genetic research, however, indicates that domesti- 

 cation has occasioned the preservation rather than the 

 origin of the fundamental variations involved. But to 

 what extent man through selection is able to modify the 

 fundamental variations which nature occasionally pro- 

 duces as sports is still an open question. Evidence is 

 nevertheless accumulating that certain of these funda- 

 mental variations may occur in two or more alternative 

 forms, and the question then arises (1) whether these al- 

 ternative forms have arisen independently by distinct acts 

 of mutation, or (2) whether one has arisen from another 

 by a process of secondary mutation, or (3) whether one 

 may not have been transmuted into another by a more or 

 less gradual process. Toward the testing of these sev- 

 eral hypotheses much genetic research is now being di- 

 rected. The first step to be taken is evidently to ascertain 

 in how many alternative forms the same fundamental 

 variation may occur and how these forms are inter- 

 related. A further step will be the attempt to produce 

 new alternative forms at will. It is our purpose, in this 

 paper, to discuss a newly discovered alternative form 

 (allelomorph) of the gray, or agouti, type of coat found 

 in wild rabbits. It occurs in the variety known as black- 

 and-tan. 



This variety appears to have arisen from the wild gray, 

 or agouti, type without the loss of any known genetic fac- 

 tor, but by a modification in one. Simple loss of genetic 

 factors is believed by most students of genetics to have 



