68 BREEDING 



Mendel himself made sixty crosses betvv^een romid- 

 seeded and wrinkled-seeded varieties on fifteen plants. 

 The second hybrid generation consisted of 7,324 

 seeds, of which 5,474 were "round or roundish," 

 and 1,850 were wrinkled ; 565 of the rounds were 

 tested ; 193 gave rounds only, 372 rounds and 

 wrinkled in the ratio of three to one. 



The seven pairs of characters of the culinary pea 

 experimented with by Mendel have now been dealt 

 with. In all of them the mode of inheritance is 

 essentially the same. Two organisms differing in 

 respect of a single pair of characters produce, 

 when mated, a hybrid, which manifests the so- 

 called " dominant " member of that pair to the 

 more or less complete exclusion of the recessive one. 

 Dominance, however, is an unessential feature of 

 Mendelian inheritance. Mendel himself stated that 

 one member of each of his seven pairs was completely 

 dominant over the other of that pair. But it is now 

 known that, in the case of the texture of the pod, the 

 hybrid between the hard and the soft bears pods of 

 intermediate texture. And we shall see later that, 

 in the case of the very first pair of characters in 

 Mendel's list, the round cotyledons of the hybrid 

 produced by crossing a round with a wrinkled-seeded 

 pea are only superficially indistinguishable from 

 those of the pure round; and that a fundamental 

 difference between them can easily be demon- 

 strated. 



The essential feature of the Mendelian phenomenon 

 is that which the mode of inheritance of the seven pairs 



