THE MUTATED GENE 125 



schmidt and Pariser, 1923, added the cytological facts later.) 

 Much clearer was the demonstration in Drosophila by Bridges 

 (19216, 1922), where different quantities of autosomal and sex 

 genes may be secured, among them the ratio 3.4 :2X producing 

 intersexes. Hen 1 , then, the actual quantities of genes con- 

 tained in visible numbers of chromosomes were shown to account 

 for the abnormal development called intersexuality. Since that 

 time, other similar cases have been found (for details, see Gold- 

 schmidt, 1931d). The generalizations derived from this analysis 

 in regard to the nature of the gene and the multiple allelomorphs 

 belong to a later theoretical chapter along with the discussion 

 of some rather naive criticisms. Here we are interested to know 

 whet her other facts exist that prove that the action of the gene is, 

 ceteris paribus, proportional to its quantity; that an orderly 

 series of quantities will lead to the typical effects seen in series of 

 multiple allelomorphs; and that there is a relation between 

 gene quantities and velocities of gene-controlled reactions of the 

 type found in chemical reactions; and finally to learn whether 

 facts exist to show generally that the quantity of a gene is one of 

 its important properties. 



A. Differences of Dosage Produced by the IX — 2X 



Conditions 



It is obvious that the mechanism of the sex chromosomes 

 permits not only" the study of sex genes in different quantities 

 but also the study of all sex-linked genes in one or two doses. In 

 the overwhelming majority of cases, one sex-linked gene in the 

 heterozygous sex has the same effect as two in the homozygous 

 sex or even a larger effect upon the phenotype. But there are 

 also a few cases known in which the haplo-effect effect is weaker 

 than the diplo-effect. Before discussing these facts and their 

 meaning, we want to point out another set of facts that is perti- 

 nent to this problem. 



1. Sex-controlled Phenotype. — There are numerous examples 

 to show that one and the same genotype, except for the sex 

 chromosomes, has a very different phenotypic expression in both 

 sexes. We leave aside for the moment everything described as 

 secondary sex characters and consider only cases of mutant genes 

 outside the sex chromosomes, therefore present in both cases in 

 duplex condition. There are innumerable cases in which such 



