THE MC TAT ED GENE 107 



Temperature shocks, finally, have also been found to influence 

 dominance even in cases of complete dominance, where ordinary 

 temperature effects are powerless. The heterozygous ebony 

 flies (Drosophila) will show a certain amount of the recessive 

 melanism if the larvae have been treated with temperature 

 shocks (36 to 37°); in heterozygous vestigial flies, the same 

 treatment might produce erect scutellar bristles which is one 

 of the recessive traits of the vestigial fly (Goldschmidt, 19356). 



B. DOMINIGENES 



For a long time it has been known that dominance may be 

 affected by the presence of other genes acting as modifiers for 

 dominance (conditioned dominance.) These genes might have a 

 visible mutant effect besides this modifying action, and they 

 might also be without any other visible effect. When it is 

 impossible to separate such genes, they are sometimes spoken 

 of as the general genie environment (Tchetverikoff). As a short 

 term for such modifying genes, Goldschmidt (19356) has pro- 

 posed the word dominigenes. Bridges (1913) found that colored 

 eyes in Drosophila were incompletely dominant to white in the 

 simultaneous presence of the genes vermilion and pink. Lance- 

 field (1918a) found in Drosophila a third-chromosome gene 

 (semiforked) which shifts the dominance of Wild over forked 

 toward the forked side. Landauer (1933) found a dominigene 

 for the frizzle character of fowl, and Dunn and Landauer (1934) 

 showed that dominigenes exist that shift the type of the hetero- 

 zygote for Rumpless (a dominant mutation) toward the normal 

 type. Lebedeff (1932) found for D. virilis that the recessive 

 gene ruffled acted as a dominant in the presence of another gene 

 rounded. Crew and Lamy (1932) found a similar case for 

 D. obscura: the gene purple acts as a dominigene upon the 

 hetero zygote -j- /vermilion, vermilion being recessive. These 

 last-named authors — the author believes the only ones — try to 

 give for this action an interpretation, to which however we are 

 unable to agree. They believe that genes in other loci may have 

 exactly the same action as the pair of genes studied. Their 

 presence might therefore interfere with dominance by an act of 

 quasi allelomorphism. As in such a case three Nonwild-type 

 genes would be present in the heterozygotes, the effect might 

 become visible in the form of what looks like change of dominance 



