SCHEMATIC REPRESENTATION MENDEL S LA W 343 



there are dominants which breed true to the dominant character, 

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

 may be cahed impure, and which on self-fertihsation (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^, P^, P^ for the parental, grandparental, and great - 

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

 tions ; F2, F^, F* 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. 



D R . . P3 — great-grandparental generation. 



I i 



D R . . P2 — grandparental generation. 



I I 



D R . . pi — parental generation. 



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



I DD 2 D(R) I RR . F2— second filial 



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



dominants. 



DD I DD 2D(R) I RR RR . F^— third generation. 



DD DD I DD 2D(R) i RR 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. 



