Hybridization and Selection 



287 



hybrid generation is called among breeders the " first filial '' 

 (Latin : filialis, related as a child), or Fi generation. 



Mendel concluded from this and many similar experiments 

 that in any pair of contrasting characters one usually appears 

 to be unmodified by the other. In other words, one of the two 

 characters shows in the Fi plants, and the other does not. In the 

 experiment with peas cited above, tallness dominates over dwarf- 

 ness. Mendel, therefore, called that character which appeared in 

 the Fi generation dominant, and the contrasting character which 

 did not appear recessive. Working further with peas, Mendel 

 discovered that purple flowers are dominant over white flowers, 

 smooth seeds over wrinkled seeds, and yellow seeds over green. 



The second important fact brought out by Mendel is that when 

 the Fi plants are self-pollinated and the resulting seeds planted, 

 an F2 generation is obtained in which both tall and dwarf plants 

 occur. Furthermore, there is a definite ratio of 3 to i between the 

 number of tall and dwarf plants. The results of these experi- 

 ments may be expressed in the following diagram : 



(Pollen parent) 

 TaU 



X 



(Ovule parent) 

 Dwarf 



Fi generation = 

 Self-pollinating 



F2 generation = 



Self-pollinating 

 F3 generation = 



All Tall 

 (Tall X Tall) 



/ 1 \ \ 



(A) 

 Tall 



I 



+ 



Pure Tall 



Always breeds 



true 



(B) 

 Tall 



(B) 

 Tall 



(C) 

 Dwarf 



\ \ \ 



3 Tall and 3 Tall and Pure Dwarf 

 I Dwarf I Dwarf Always breed 



true 



Evidently the factor for dwarfness is carried along with the 

 factor for tallness in the Fi generation, but the tallness dominates 

 it and the dwarfness does not show. In the F2 generation there 



