The F2 generation :- 



Female 

 Gametes 



= male gametes 



= 12 white 

 (flecked). 



3 colored 



1 white. 



(See Punnett's Mendelism). 



Morgan has shown in the case of Drosophila that the 

 presence of certain specific factors produces sterility, and 

 Bateson has found a definite factor for pollen atrophy in 

 sweet peas, which behaves in a Mendelian manner. 



With regard to self-sterility in beans Belling has pro- 

 posed a Mendelian explanation {Journal of Heredity, 1914, 

 1916). When he crossed two fertile races of beans, Florida 

 Velvet and Lyon, the hybrids were semi-sterile. In the F2 

 generation, however, one-half of the plants had perfect 

 pollen and ovules, the other one-half had a mixture of equal 

 numbers of good and bad pollen grains and ovules. In the 

 F3 generation the progeny of the fertile plants had good 

 pollen and ovules, but that of the semi-sterile was like F2. 



Belling proposes the presence (or absence) of a fertility 

 (or sterility) factor A, a in race X and another similar 

 factor B, b in race Y. 



If the Velvet Bean possesses the factors A Abb, and the 

 Lyon Bean the factors aaBB where A and B are factors for 

 fertility and a and b are factors for sterility, the gametes for 

 the former will be Ab and for the latter aB. The Fi genera- 

 tion will have the factor-constituents AaBb which render it 

 semi-sterile. The gametes of the F| generation will be AB, 

 Ab, aB, ab, but if AB and ab are lethal to pollen grains and 

 ovules the F2 generation will be represented by the follow- 

 ing diagram. 



Aa 



aB 



Aa 

 aB 



or 50% fertile and 50% semi-sterile. 



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