49 ZOOLOGY 



Mendel hybridized varieties of garden peas. One true- 

 breeding variety is dwarf and another tall. When these are 

 artificially crossed, no matter which variety furnishes the pollen, 

 all the offspring are like the tall parent in height. The dwarf 

 quality, which evidently must be represented in the offspring, 

 does not show in the body at all. He therefore concluded that 

 tallness was dominant over dwarfness. Dwarfness is said to be 

 recessive. 



FIG. 252. 

 TALL (pure) X DWARF 



TALL.. 



(Hybrid) 



self-bred 



^ s 



TALL ( 3 ) DWARF ( i ) . . . . F 2 



/ i I 



TALL (i) TALL (2) DWARF F 3 



(pure) (hybrid) (all) 



FlG. 252. Diagram illustrating Mendel's results in breeding tall and dwarf peas. Pi, Fz, F, 

 firtt, second, and third filial generations. The first generation are all tall; but we know they are 

 impure (hybrid) both because we know the parents, and by their offspring when bred among them- 

 selves. The dwarfs (recessive) when they once appear are necessarily pure, and breed true. The 

 tails of Fj generation are of two kinds as shown by their offspring, i pure to 2 impure. The figures 

 in parenthesis indicate relative numbers. All generations after F, are self-bred. 



When these tall hybrids were self -fertilized, three-fourths of 

 their offspring were tall like the parents, and one-fourth were 

 dwarf like the dwarf grandparent. In the case of the dwarf 

 offspring the parents clearly transmit something which the 

 parent body does not possess. There were no intermediate 

 forms. Further breeding showed that these dwarfs were pure 

 dwarfs with no taint of tallness on them ; for when self -fertilized 



