THE MVTATED GENE 163 



gene in question is irrelevant.) The}' arc lethal when homo- 

 zygous; and all of them, scattered over all chromosomes, have a 

 similar phenotypic effect, viz., shorter bristles, blunter wings, 

 plexus venation, smaller size, slow development, larger and rough 

 eyes, poor viability. Schultz argued that a combination of two 

 Minutes ought to give a lethal effect or at least an extreme 

 phenotype if all are concerned with the same primary reaction, 

 i.e., ought to give an additive effect. No combination gave such 

 a result. To test whether an all-or-none or threshold effect 

 was involved Schultz made experiments that led to the following 

 observations : 



1. A duplication suppressing a known Minute effect at the same 

 section of the chromosome does not influence another Minute 

 effect at a different locus. 



2. One Minute is recessive to two normals in triploids. Two 

 simultaneous but different Minutes do not change the situation. 



3. Two of the same Minutes in a triploid, however, are lethal. 

 From such facts Schultz concluded that no threshold effect can 



be involved and the different Minutes do not affect the same 

 primary reaction. He then combined different Minutes with 

 different allelomorphs of Delta, which has a phenotypic effect 

 that is roughly the contrary of Minute. A combination Delta- 

 Minute is either an extremely abnormal individual or lethal. 

 This effect varies quantitatively in proportion to the effect of 

 the Minute involved. And it varies also in proportion to the 

 grade of the Delta allele; the highest alleles produce, in this 

 combination, lethality; the next lower one, early death of the 

 thoroughly abnormal fly; the next lower one, later death; and 

 the lowest member, an abnormal fly not capable of hatching. 

 Similar effects were produced in combination with other genes, 

 showing that the effect of the Minutes concerned in these results 

 (the secondary reaction of Schultz) is quantitatively different in a 

 definite seriation of Minutes. This applies to measurable 

 characters like viability and bristle length within the series of 

 Minutes and the parallel series of combinations with other 

 genes. Schultz accounts for these facts by the assumption that a 

 reaction exists in development, in which a great many genes are 

 involved; and that changes in any of these contributors may set 

 off a secondary reaction, the Minute reaction. This would then 

 illustrate one of the possibilities of genie interactions, as outlined 



