SCHEMATIC REPRESENTATION MENDEL S I A IV 343 



there are dominants which breed true to the dominant character, 

 and are therefore pure ; and thirdly, there are dominants which 

 may be called impure, and which on self-fertilisation (or in-breed- 

 ing, where the sexes are separate) give both dominant and re- 

 cessive forms in the fixed proportion of three of the former to one 

 of the latter." 



Schematic Representation of Mendel's Law. — Following Mr. 

 Punnett's suggestion, with slight modifications, we may use 

 the symbols P 1 , P 2 , P 3 for the parental, grandparental, and great- 

 grandparental generations ; F 1 for the first filial (hybrid) genera- 

 tions ; F 2 , F 3 , F 4 for the subsequent inbred generations. The 

 symbol D(R) means a dominant with the recessive character 

 unexpressed, but potentially present ; DD or RR means pure 

 " extracted " dominants or recessives — i.e. those pure forms 

 which are sifted out from the inbreeding of " impure " dominants. 



. P 3 — great-grandparental generation. 

 . P 2 — grandparental generation. 

 . P 1 — parental generation. 



D(R) . . F 1 — first filial (hybrid) generation. 



1 



1 



1 DD 2 D(R) 1 RR . F 2 — second filial 



"Extracted " pure Impure dominants. Pure recessives. (inbred) generation, 



dominants. 



I I I I 



DD 1 DD 2D(R) 1 RR RR . F 3 — third generation. 



I I I 



DD DDiDD 2D(R) iRR RR RR . F*— fourth generation. 



§ 2. Theoretical Interpretation 



Mendel was not content with formulating his results in a 

 law ; he advanced a theoretical interpretation which is at once 

 ingenious and simple. 



