CHAPTER IX 



THE NATURE OF THE MENDELIAN PAIR OF CHARACTERS 



A QUESTION which naturally and frequently presents 

 itself to the mind is : " What is it that makes one 

 character dominant over another when they meet 

 in a cross ? " A common answer to this question 

 is that the dominant character is strong and the 

 recessive one is weak ; but this is too vague a notion 

 to be of the nature of an explanation ; moreover, 

 it is, in fact, little more than a restatement of the 

 difficulty involved in the question. 



Before proceeding to the two theories which 

 appear to be worthy of consideration, I think it is 

 desirable to warn the reader against an idea, which 

 has found its way into print, that there is some 

 connection between selection and dominance ; that 

 a dominant character is the result of a long process 

 of selective breeding. There is no ground whatso- 

 ever for such an idea, and it is difficult to imagine 

 how it can have arisen. 



Two theories of the nature of the Mendelian pair 

 of characters, and of the cause of dominance in parti- 

 cular, have obtained wide credence. One of them 

 has already been exploded, the other is still supported 

 by a considerable party of adherents. 



The first of these is the idea that the oldest of 



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