HYBRIDIZING PLANTS 



125 



(usually designated as Fi, first filial generation) consisted 

 of nothing but tall plants. These plants were permitted to 

 be self-fertilized, and a second (F2) generation was obtained. 

 This generation consisted of some tall and some dwarf 

 plants. Thus, Mendel showed that the dwarf character was 

 not lost in the cross, but was transmitted from the parent to 

 the second generation even though it was not expressed in 

 the first generation. Since the tall character masks the dwarf 

 character in the Fi, it can be said to be dominant to dwarf. 

 Conversely, dwarf is recessive to tall. The principle of domi- 

 nance is of great importance in plant breeding, but all charac- 

 ters are not necessarily dominant or recessive. 



Important as this discovery of dominance was, Mendel's 

 analytical method led him to a still more important dis- 

 covery. He not only observed that the second generation 

 had both tall and dwarf plants, but he counted up how many 

 of each. His F2 generation consisted of 787 tall plants and 

 277 dwarf plants. This is a ratio of 2.84 to 1 or approxi- 

 mately 3 to 1. His second experiment, crossing a plant with 

 smooth seeds with one with wrinkled seeds gave similar 

 results. The Fi consisted of plants all of which had smooth 

 seeds. The F2 consisted of 5,474 plants with smooth and 

 1,850 plants with wrinkled seeds or a ratio of 2.96 to 1. 

 Again the approximation is 3 to 1. The results of the other 

 experiments were similar. In each pair of characters, one 

 was dominant in the Fi, and the F2 consisted of approxi- 

 mately 3 dominants to one recessive. The results of all seven 

 experiments are shown in the following table: 



Nature oj Character Dominant Recessive Ratio 



Height of plant 787 tall 277 dwarf 2.84-1 



Shape of seed 5474 smooth 1850 wrinkled 2.96-1 



Color of flowers 705 colored 224 white 3.15-1 



Color of cotyledons 6022 yellow 2001 green 3.01-1 



Type of pod 882 inflated 299 constricted 2.95-1 



Color of pod 428 green 152 yellow 2.82-1 



Position of flower 651 axial 207 terminal 3.14-1 



Total 



14949 5010 2.98-1 



