384 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



The dominants, however, were not all pure dominants, for when 

 they were allowed to self-fertilise they produced one-third pure domi- 

 nants and two- thirds "impure" dominants, the latter being distin- 

 guished by the fact that in their offspring recessives reappeared in the 

 proportion of one recessive to three dominants. 



The outstanding facts, taking the case of yellow-seeded and green- 

 seeded peas, may be thus summarised: 



Parental 



Generation (Pi) 



Yellow-seeded "pure" 

 plant (dominant) 



Green-seeded "pure" 

 plant (recessive) 



First Filial (hybrid) 

 Generation (Fi) 



All the offspring were yellow-seeded 

 Self-fertilised they yielded 



Thus intercrossing of forms with contrasted characters results not 

 in transitional blends, but in the dominance of one character and the 

 recession of another. Self-fertilisation (the extreme of inbreeding) 

 of the hybrids results in a number of pure recessives and a number of 

 dominants in the proportion 1:3; some of these dominants (one-third) 

 are pure, and produce only dominants; some (two- thirds) are appar- 

 ently pure, but produce dominants and recessives hi the old propor- 

 tion, 3:1. 



A case of mice. Let us take a concrete case from among animals. 

 A grey house-mouse is crossed with a white mouse; the offspring are 

 all grey. Greyness is dominant; albinism is recessive. 



i G 2 G(W) 



i W 



