THE ENGLISH BABBIT AND THE QUESTION OF 

 MENDELIAN UNIT-CHABACTER CONSTANCY 



W. E. CASTLE AND PHILIP B. HADLEY 1 



Whatever the theoretical importance of Mendel 's law, 

 its practical utility depends largely upon the purity of 

 the gametes. If Mendelian unit-characters can through 

 hybridization be recombined in desirable ways without 

 essential modification during the process, Mendel's law 

 is evidently a distinct acquisition to the practical breeder. 

 Nevertheless, if crossing is likely to produce considerable 

 changes in the characters which it is desired to combine 

 in a new race, it is evident that Mendelian crosses must 

 be used judiciously and with caution by the practical 

 breeder. 



Considerations such as these have led the senior author 

 for several years to concentrate his studies of genetic 

 problems upon the question of gametic purity. As a 

 crucial experiment he conceived the plan of deriving an 

 entire race of animals, not from a single pair of ancestors, 

 but from a single gamete, so far as concerns a particular 

 unit-character. It was thought that in a race so derived, 

 if the principle of gametic purity holds, there should be 

 no variation whatever in the particular unit-character 

 concerned. 



Color patterns of mammals seemed especially well 

 adapted for such studies, since they are early differen- 

 tiated and clearly Mendelize in crosses. The so-called 

 ' 1 English" piebald rabbit presents an especially fine 

 example of such a color pattern. The figures give a 

 good idea of this striking pattern in which white and 

 colored areas are interspersed much as in the "coach- 



i Joint publication of the Laboratory of Genetics of the Bussey Insti- 

 tution, Harvard University, and of the Agricultural Experiment Station 

 of the Rhode Island State College (Contribution 211). 



