130 EVOLUTION 



and dwarfs in the 3 : 1 proportion. Thus the 

 F 2 generation, resulting from the self-fertili- 

 zation of the cross-bred forms or hybrids (Fj), 

 consisted of 25 per cent, pure dominants, 50 

 per cent, impure dominants, and 25 per 

 cent, pure recessives. 



The results may be expressed in a scheme : 



Parental generation Tall variety Dwarf variety 



! . I 



First filial (hybrid) all the offspring tall ; self- 



generation (Ft) fertilized they yielded 



Second filial (inbred) 25% Tails 50% Tails 25% Dwarfs 



generation (F 2 ) (pure dominants) (impure dominants) (pure recessives) 



I 



I ~T~ I 



25% 50% 25% 



Tails Tails Tails Dwarfs Dwarfs 

 (pure) (impure) (pure) 



Or, using D for the forms with the domi- 

 nant character, R for the forms with the re- 

 cessive character, and D(R) for forms with 

 the dominant character expressed and the 

 recessive character latent, the facts may be 

 expressed in a more generalized way thus 

 (after Punnett) : 



Parents <*" D R 



First filial generation (Fj) D (R) 



I I 



ID + 2D(R) -}- 1R 

 Second filial generation (F 2 ) (pure (impure (pure 



dominants) dominants) recessives) 



I I I 



Third filial generation (F s ) D ID + 2D(R) + 1R R 



Let us take as an illustration from among 

 animals, one lately well illustrated in the 



