j 4 2 EXPERIMENTAL STUDY OF INHERITANCE 



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 apparently pure, but produce 

 dominants and recessives in the old proportion, 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. 



The grey hybrids are inbred ; their offspring are grey and white 

 in the proportion 3:1. If these whites are inbred they show 

 themselves " pure," for they produce whites only for subsequent 

 generations. But when the greys are inbred they show them- 

 selves of two kinds, for one-third of them produce only greys, 

 which go on producing greys; while the other two-thirds, ap- 

 parently the same, produce both greys and whites. And so it 

 goes on. 



(Pi) 



G(W) 



(F 1 ) 



1 G 



2GXW) 



1 w 



1 



(F 2 ) 



iG 



2 G(W) 



1 W 



W 



(F3) 



Summary. — In his exceedingly clear exposition of Mendelism 

 (1905) Mr. R. C. Punnett states the result thus : " Wherever 

 there occurs a pair of differentiating characters-, of which one is 

 dominant to the other, three possibilities exist : there are 

 recessives which always breed true to the recessive character ; 



