VARIATION AND HEREDITY 131 



3 : 1 proportion. Thus the F 2 generation, re- 

 sulting from the self-fertilization 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 



Pirtt filial (hybrid) all the offspring: tall ; self- 



generation (FJ f ertilized they yielded 



Talla 



Sewidfilial(inbred) 25 2 Tails 60% Talla 25% Dwarfs 



generation (Fg) (pure dominants) (impure dominants) (pure recessives) 



25% 50% 25% 



Tails Tails Tails Dwarfs Dwarfs 



(pure) (impure) (pure) 



Or, using D for the forms with the dominant 

 character, R for the forms with the recessive 

 character, and D(R) for forms with the 

 dominant character expressed and the reces- 

 sive character latent, the facts may be 

 expressed in a more generalized way thus 

 (after Punnett) : 



Parentt D R 



First filial generation (F^ D(R) 



ID + 2D(R) + IB 



Second filial generation (Fa) (pure (impure (pure 



dominants) dominants) recessives) 



Third filial yentration (F s ) D 1D + 2D(R) + 1R R 



Let us take as an illustration from among 



animals, one lately well illustrated in the 



E2 



