THE MUTATED GENE 129 



looks like a female A A (the mutant genes are dominant); a male 

 AAbb like a female AABb; etc. This applies as well to the 

 autosomal as to the sex-linked genes, since males with the sex- 

 linked gene in heterozygous condition are much darker than 

 females in simplex condition. Goldschmidt interpreted these 

 facts by saying (1920, page 95): The cause must be sought in the 

 physiological phenomena of pigmentation. Exact knowledge is 

 lacking but the facts indicate that the genes for pigmentation 

 control a definite increase in the quantity of pigment and that a 

 given quantity covers the small wing of the male faster than the 

 larger wing of the female. A better description would have to be 

 given in the terms used above. 



A similar example is also available from the work on the 

 vestigial character of Drosophila (Goldschmidt, 1935-1937). 

 Here, as described on page 109, a series of three mutant genes 

 (dominigenes) shift the phenotype of the vg/A- heterozygote 

 toward scalloped wings, and again the three genes, one of which 

 is sex linked, have an additive effect. The effect, however, 

 requires the presence of both dominant autosomal genes at least 

 once in the female (AaBb), whereas males of the constitution 

 A A bb show the same effect. This case is of interest because many 

 of the facts concerning development, phenocopies, and multiple 

 alleles are known and furnish just such a system of develop- 

 mental processes as is required for the explanation of the phe- 

 nomenon with which we are concerned here. 



A fourth group of facts which belong here are the facts con- 

 cerning sex-controlled heredity. This term (Goldschmidt, 

 1920a) means that the phenotypic effect of mutant genes is 

 suppressed in one sex, i.e., is controlled by the specific features of 

 sexual development. (It partly covers the older term sex 

 limited.) Its actual basis can best be demonstrated in certain 

 crosses of L. dispar. There are mutants existing in regard to the 

 wing color of the male, not visible in the female. In a backcross 

 or F 2 involving such mutants, the females are all alike; the males 

 show the simple segregation as expected in all such cases of 

 crossing with sex-controlled traits. If the cross, however, is such, 

 a one that the females become intersexual and assume male wing 

 color, the segregation is also visible on the wings of the intersexual 

 females (Goldschmidt, 1920c). A number of instances of sex- 

 controlled heredity are known partly with very large phenotypic 



