CHAPTER X 

 NON-MENDELIAN INHERITANCE 



Up to this point Mendelism and its various modi- 

 fications have been considered, and the impression to be 

 gained thus far is as follows. Mendel's law as originally 

 stated is clear, reasonable, and well established. There 

 have appeared certain types of inheritance which have 

 seemed at first sight to contradict Mendel's law; but 

 practically all of these later have been shown to be con- 

 sistent with that law. The conclusion, therefore, may 

 be that Mendel's law is firmly established but that its 

 expression is not always so simple as was once sup- 

 posed. Illustrations have been given showing how 

 Mendelian explanations must be based frequently upon 

 numerous factors of various types. The impression, 

 therefore, may be that Mendelism is so established and 

 its application so universal that it explains every type of 

 inheritance that is known or that ever will be known. 

 It is true that Mendel's law is dominant with most 

 geneticists as explaining most of the known facts of 

 inheritance, although there are certain types of inherit- 

 ance that have not been explained as yet quite satis- 

 factorily in this way. As a consequence, a number 

 of prominent geneticists protest against the universality 

 of the law. These unexplained phenomena must now 

 be considered under what may be called non-Mendelian 

 inheritance. It will be recalled that EMERSON and 

 EAST stated that only two indisputable cases of non- 

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