ARE RECESSIVES LOSSES OF GENES? 93 



taken place independently from the wild type ; 2 but it is 

 possible to interpret absence in such a way that it is not 

 in contradiction with the occurrence of multiple allelo- 

 morphs. Suppose, for instance, that different quantities 

 of materials are lost at the locus in question for each 

 mutant type. The loss of one quantity might stand for 

 white, another quantity for cherry, and so on. The result 

 might then not appear to be inconsistent with the facts, 

 although it should be noted that the assumption calls for 

 a somewhat different interpretation of the gene as a unit. 

 The ' ' compound ' ' formed by the presence of two of these 

 allelomorphs might then not be expected to give the wild 

 type but something else. To admit this, however, changes 

 the idea of presence and absence in such a way as to make 

 it essentiallv the same as the view that is here main- 

 tained, namely, that mutation is due to a change of some 

 sort in a gene. There is no advantage, that I can see, in 

 urging that the change must be a loss of part of the gene 

 (gene meaning a quantity of something at a given locus). 

 This is a gratuitous assumption in regard to the nature 

 of the change — one that is not necessary to explain the 

 results. It may be, of course, that a gene may be lost or a 

 part of a gene may be lost and a new mutant result, but 

 it is theoretically possible that the constitution of the 

 gene may change in some other way. So long as we do not 

 know anything definite concerning the kind of change 

 that takes place there is nothing to be gained by limiting 

 it to only one kind of process. 



2 If the multiple allelomorphs had arisen seriatim, i.e., one from another, 

 then of course it might be possible that each one carried the preceding 

 mutant gene. If so the two when crossed would not give the wild type. But 

 when, as in Drosophila, each has arisen independently from the wild type 

 the situation is different, as explained in the text. 



