CHAPTER VII 



SOME APPARENT EXCEPTIONS 



Many of the cases of inheritance that at 

 fir^t appeared to be exceptions to MendeFs 

 law are found to be explicable by it, and really 

 strengthen our belief in its accuracy and univer- 

 sality. Thus several years ago Bateson, one 

 of the foremost English investigators, crossed 

 two sweet pea plants that bore white blossoms. 

 Strangely enough, the offspring were plants that 

 had purple blossoms. The plants reared from 

 the seed of these purple-flowered kinds were 

 part purple, part white, in the proportion of 

 9 to 7. Bateson recognized in this the familiar 

 Mendelian ratio of 9-3-3-1, though the last 

 three terms have united to produce the 7. 

 The normal Mendelian ratio indicates that at 

 least two factors are involved, and Bateson 

 conceived that the purple character is really 

 dependent upon two factors, and that both 

 must be present to produce it. One of the 



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