ALLELOMORPH 1C RELATIONSHIPS IN MENDELISM 



145 



gations with Drosophila 

 indicate that usually a 

 normal allelomorph is dom- 

 inant to a mutant factor, 

 and in fact often to the 

 eye completely dominant. 

 More precise investigations 

 indicate, however, that al- 

 though for all practical 

 purposes dominance often 

 is so complete as to closely 

 approximate the expres- 

 sion of the homozygous 

 character due to the 

 duplex condition of the 

 dominant factor, still the 

 completeness of dominance 

 is often more apparent 

 than real. 



Darbishire has attacked 

 this problem in the case of 

 the cross smooth as con- 

 trasted with wrinkled peas. 

 Mendel's experiments 

 showed that smooth or 

 round shape is dominant 

 over the wrinkled shape in 

 peas and as in other cases 

 the dominance appears to 

 the eye complete. Darbi- 

 shire investigated the cause 

 of the difference between 

 round and wrinkled peas 

 and found it associated 

 with a difference in starch 

 content. Thus during the 

 development of the seed 

 in those races possessing 

 round seeds the sugar is 

 almost wholly converted 

 into starch so that when 

 the seed is ripe and drying 

 it retains water rather 

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