82 THE THEORY OF THE GENE 



of them (Fig. 46b) is vermilion despite the fact that one 

 normal allelomorph of vermilion is present in the piece. 

 At first sight it may seem, if the vermilion genes are 

 interpreted as absences, that two absences cannot pos- 

 sibly dominate one presence. On second thought, how- 

 ever, another explanation is possible, for, if the vermilion 

 eye color is due to the action of all the other genes when 

 vermilion is absent, the same result might happen even 

 though one dominant normal allelomorph is present. The 

 situation is not identical with one in which a vermilion 

 gene is present in one chromosome and its normal alle- 

 lomorph in the other. 



The relation shown here between two recessive genes 

 and a dominant gene in the translocated piece does not 

 always lead to the development of the recessive charac- 

 ter. For example, there is another case of translocation 

 reported by L. V. Morgan. A piece of an X-chromosome 

 of the region of the mutant genes yellow and scute be- 

 came stuck to the right end of an X-chromosome. A 

 female that has the recessive genes for yellow or for 

 scute in each of her X-chromosomes (Fig. 46c) and a 

 piece attached to one of these X's shows the wild type 

 character. Here the effects of the recessive genes are coun- 

 terbalanced by the dominant allelomorphs of the attached 

 piece. This is interpreted to mean that all the other genes, 

 plus those in the attached piece, combine to turn the scale 

 toward the dominant type and this is expected on either 

 of the contrasted interpretations as to the nature of the 

 gene. 



The relation of two recessive genes to one dominant 

 has also been studied in the triploid endosperm of corn 

 and in one triploid animal. The nuclei of the endosperm 

 cells of the seed of corn arise from the union of one pollen 

 grain (haploid in chromosome number) and two nuclei of 

 the embryo sac (each haploid). A triploid or threefold 



