Chromosomes and Genes 157 



a scale at least ten times cruder than in a salivary chromosome, 

 could never be seen. We mentioned also the substructure of salivary 

 bands as seen in the electron microscope (I 2 A), 



It is quite possible, even probable, that the older view of Stadler 

 (see 1933) that mutants are deficiencies will turn out to be correct 

 as far as point mutations are concerned, or at least for many point 

 mutations. As long as we thought in terms of genes, this view en- 

 countered great difficulties because of the series of multiple alleles at 

 one locus, dosage eflFects, and so on. These diflBculties have completely 

 disappeared, since we know that deficiencies can produce a position 

 ejffect and that known position efl[ects act as multiple alleles to each 

 other as well as to point mutations. This identity includes dosage 

 effects. The meaning of multiple allelism has become completely 

 independent of the assumption of a corpuscular gene. Furthermore, 

 the dosage effects do not pose any more difficulties since Stern showed 

 that R( + ) ci ci acts as if it were ci ci ci; that is, a position effect 

 substitutes for a mutant in dosage experiments. The most powerful 

 argument is derived from the homozygous deficiencies. It has been 

 mentioned that in Drosophila a homozygous deficiency for yellow has 

 the phenotype yellow, and many other examples were registered. 

 Recently McCHntock (1951) mentioned again the same behavior for 

 a large series of loci in maize. Hence it is clear that we are dealing 

 with a fact which is not isolated. Whereas in these cases no locus or 

 gene is present, we can only conclude that the change of order of 

 structure within the chromosome from abcdefg to abcefg is respon- 

 sible, which can be called a position effect if a position effect is not 

 an action of a locus near a break but rather the action of a change in 

 order within the chromosome. If we remember, further, aU that was 

 said on X-ray and ultraviolet-induced deficiencies and point mutants, 

 it becomes clear that point mutants are not only position effects of 

 tiny rearrangements but that, specifically, many or possibly most of 

 them are tiny deficiencies of chromosome material. However, this 

 cannot be true where the exaggeration phenomenon is found, which 

 requires a point mutant different from a deficiency. 



Liining ( I952a,b ) , like others before him, has tried to establish a 

 difference between radiation-induced "gene mutations" and rearrange- 

 ments (see also Bonnier and Liining, 1951). He showed that ir- 

 radiation during spermatogenesis in Drosophila results in different 

 effects according to whether sperm is used 1-6 days after treatment or 

 7-10 days after. In the latter, many more breaks were produced 

 leading to hyperploids and gynandromorphs. When a chromosome 



