THE MUTATED GENE 123 



genes may be terminated by the effects of other developmental 

 processes while still very incomplete. Wright (1934) also comes 

 to the same conclusions. 



But another point derived from physiological genetics has also 

 entered this discussion. In the vestigial case, we (Mohr and the 

 author) found that it must be assumed that within the Wild 

 phenotype many different degrees of Wildness must exist, all 

 appearing alike on account of the threshold conditions, a view 

 that had originally been derived in another field by Goldschmidt 

 from the analysis of intersexuality for different grades of maleness 

 or femaleness. In discussing Fisher's work, Haldane (1930) 

 points out that selection might also have selected instead of 

 modifiers, more potent Wild-type genes (what we called Hyper- 

 wild, far above the threshold). Muller (1932) set out to prove 

 the existence of such Wild-type genes in different potencies. He 

 used the findings of Timofeeff (1932) that a Russian race of 

 Drosophila showed a different rate of mutation to white eye 

 from the rate in the American race. Assuming that the Wild 

 allelomorphs in this case may actually be different, Muller com- 

 bined both of them with two white eye genes in a triploid con- 

 dition (attached X's). He found that the American gene was 

 less dominant than the Russian and attributes this to different 

 potency, based on different levels above the threshold. We shall 

 meet the same set of facts in a later chapter. 



6. THE GENE IN DIFFERENT DOSES 



The most elementary facts of genetics require the assumption 

 that it is not irrelevant whether a gene is present in one or two 

 doses. This quantitative view found its early expression in 

 Bateson's presence-absence theory which claimed that a dominant 

 gene is the presence, and the recessive the absence, of something. 

 The heterozygote therefore contained one dose of a gene as 

 compared with the two doses of the homozygous dominant. It 

 is known that this theory has been disproved, at least in this its 

 original form. Another type of quantitative view was intro- 

 duced by Goldschmidt (1917) and claims that the quantity 

 of the thing that is called a gene is important for the result 

 of genie action and that gene and effect are linked, ceteris paribus, 

 by the simple relation of a proportion between the quantity of 

 the gene and the velocity of the chain of reactions controlled 



