An Introduction to a Biology 



All that the 50 : 50 ratio shows, if it be true, is that the 

 Mendelian explanation only accounts for what is happen- 

 ing in gametogenesis of the second generation, and we 

 should not base a general conception of heredity on the 

 conditions obtaining in the second generation. Darbishire 

 obtained seeds from many sources, with the result that 

 pink by white always gave purple, which means that all 

 the white are BBpp, i.e. all carry blue in a homozygous 

 condition. 



There are no pure whites on the market, if we accept 

 the Mendelian explanation. 



Darbishire does not believe that this formula gives us 

 what is really happening. He believes that the union of these 

 two characters sets up a disturbance, causing them to fall 

 back on what they used to be, while later segregation occurs. 



The degree of disturbance would be comparable to the 

 length of time the two strains remained isolated. 



Darbishire has planned and is now continuing the follow- 

 ing experiment : 



Select pure pink with formula PPbb and pure white 

 with formula ppbb. Cross these : 



PPbb X ppbb 



pink. 



Save these seeds, and in next generation make the same 

 cross : 



PPbb X ppbb 



If the Mendelian theory is correct, saving the seeds and 

 repeating this cross again and again should never give any- 

 thing but pink. However, if there is anything in the other 



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