84 



THE THEORY OF THE GENE 



in the first case, and two presences to dominate one ab- 

 sence in the second case. 



The interpretation of two absences dominating a pres- 

 ence would have no meaning if taken literally, but as has 

 been pointed out it is possible to explain such a statement, 

 if, in the absence of a gene, the floury character is deter- 

 mined by the rest of the genes, and, of course, the same 



(a) 



(a'j 



fl- 



fi 



ft 



f I O UT Y 



ft- 



-ft 



-fl 



flint 



Fig. 48. 



Diagrams of triploid condition of endosperm of corn when, as in a, 

 two floury genes and one flinty are present giving floury endo- 

 sperm; and when, as in a', two flinty genes and one floury gene 

 are present giving flinty endosperm. 



explanation applies if there is present a gene for floury 

 (a mutated gene from flinty) whose effect is produced by 

 itself plus the rest of the genes. This evidence from trip- 

 loid endosperm is no more decisive than when a trans- 

 located piece of a chromosome introduces a third element 

 into the situation. 



There are several other cases in corn where two reces- 

 sive elements do not dominate a single dominant, but 

 these have no further bearing on the present question. 



If a triploid female Drosophila has a vermilion gene in 

 each of two of its X-chromosomes and a red gene in the 

 third, the resulting eye color is red. One dominant gene 

 here dominates two recessives. This result is the opposite 



