ALLELOMORPHIC RELATIONSHIPS IN 
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 
10 
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MENDELISM 
Fre. 66.—At the left, starch grains of round pea; at the right, of the wrinkled pea; and in the middle, of a hybrid between round and wrinkled 
(After Darbishire.) 
Magnified about 300 times. 
peas. 
