I ; 1 /*// YS/nLOGICAL GENETICS 



mutant gene for rosin exes produces a smaller quantity of pig- 

 iin'iit (or a lower grade of oxidation) than the wild-type allelo- 

 morph, the seriation of decreasing quantities produced will be 

 +/+ > -V /w r > w*/W > iV; i.e., one IV leads to less pig- 

 mentation than two w'. As the condition produced by the 

 homozygous recessive w e /w" is regarded as the mutant type, 

 the effect of one 10' will be still further away from normal, i.e., 

 exaggerated in comparison with the homozygous recessive. 

 'This interpretation, which in itself is independent of the assump- 

 tion that the mutation from + to w e was a change in quantity 

 (an assumption strongly suggested by these facts), has since 

 been proved to be correct. The proofs, derived from the study 

 of the effects of more than two recessives, wdll be discussed in 

 the next chapter. They have been accepted as valid by Stern 

 (1930), Mohr (1932), and Muller (1932). The last-named 

 author has proposed to call mutations, which produce a lessened 

 effect (slow-er rate of reaction according to Goldschmidt) and 

 therefore show this dosage phenomenon, hypomorphs (which 

 seems unnecessary) and has added a number of other instances, 

 all of the same type. These facts, then, actually show that in 

 this case the effect of a gene is proportional to its quantity. 



In a considerable number of the cases studied, the facts reported 

 above led to the conclusion that the action of the mutant genes 

 consists in changing- rates of reaction of the special physiological 

 process involved in the production of the phenotype. The 

 phenomena just reported then prove that, in these cases at least, 

 the velocities of the respective reactions are, ceteris paribus, 

 proportional to the quantities of what is called a gene. This 

 proved fact might or might not justify the extension of this view 

 to the primary differences between the Wild type and the mutant 

 gene. The author's impression is that it is not at all easy to 

 evade this conclusion, but the discussion of this point belongs 

 to the chapter on the theory of the gene. It may be added, 

 however, that the majority of gene mutations, according to 

 Muller (1932), are of this hypomorphic type. 



Muller (1932) refers to a number of cases which, though 

 they show that the dosage of a gene has a typical proportional 

 effect upon the end product, yet differ in important points from 

 the simple relations just reported. He points to Mohr's work 

 on the behavior of abnormal abdomen in different doses. The 



