INHERITANCE 



289 



Mendel's next step was to follow the behavior of these charac- 

 ters in succeeding generations. Therefore the tall hybrids (Fi) 

 were inbred (self-fertilized) and their offspring, the second filial 

 (F 2 ) generation, were found to be tall and dwarf in the ratio of 

 three to one (3D : Id) . This is now a broadly established Mendelian 

 ratio. But, of course, in dealing with a small number of individ- 

 uals this ratio is merely approximate; the greater the number of 

 offspring, the closer it is approached. In this particular case Mendel 

 obtained 787 dominant and 277 recessive individuals: a ratio ap- 

 proximating 3:1. (Fig. 181 A.) 



Fig. 181A. — Inheritance of size in a cross between a tall and a dwarf race 

 of the edible garden Pea. The small circles represent the genes involved. 



Continuing the work, Mendel found that the dwarfs (recessives) 

 when inbred gave only recessives generation after generation, 

 and accordingly were pure. On the other hand, the tall plants 

 (dominants) when inbred proved to be of two kinds: one-third 

 pure dominants which bred true indefinitely, and two-thirds hy- 

 brids like their parents, giving when inbred the same ratio of 

 three dominants to one recessive in the third filial (F 3 ) genera- 

 tion. 



