PHENOMENA OF INHERITANCE 239 



offered by the peas, since in this case the mixed 

 dominant-recessives D (R) are always distin- 

 guishable from the pure dominants DD. 



In the F 2 generation and in all subsequent 

 ones the pure dominants and the pure reces- 

 sives always breed true when self-fertilized, 

 whereas the mixed dominant-recessives con- 

 tinue to split up in each successive generation 

 into pure dominants, mixed dominant-reces- 

 sives and pure recessives in the proportion 

 1 : 2 : ■ 1. The result of this is that the relative 

 number of dominants and recessives increases 

 in successive generations, whereas the relative 

 number of mixed dominant-recessives de- 

 creases, and in a few generations a hybrid race 

 will revert in large part to its parental types 

 if continued hybridization is prevented. On 

 the other hand there is no tendency for the 

 relative number of dominants to increase and 

 of recessives to decrease in successive genera- 

 tions ; an equal number of pure dominants and 

 pure recessives is produced in each generation. 



With remarkable insight Mendel recog- 

 nized that the real explanation of the splitting 

 of pure recessives and pure dominants from 



