Cases of niimio mutations and secondary mutations in tiie X-cliromosome v^(. l\ 



were singed, thus proving: that singed- was identical with or allelo- 

 m Orphic to singed. 



Singed had never been used in combination with the genes men- 

 tioned, so the possibility ol contamination is excluded. If the paternal 

 X-chromosome of the mother had carried the singed gene as a result 

 of contamination in her ancestry, then the large majoiity of her broad 

 echinus ruby sons should have been singed. And if her maternal X- 

 chromosome had contained the singed gene, her two broad echinus sons 

 should have been singed, since they arc due to crossing -over between 

 echinus and ruby. 



The fact that only a single singed- male occured proves that the 

 mutation occured in the mother at, or not more tliau a ver\- few cell 

 generations before the maturation of the egg, or even later after the eg^ 

 was formed. 



Singed- females were tested in several mass cultures by males 

 from different stocks. Like ordinary singed females the} proved to be 

 entirely sterile. Unfortunately the egg alteration caused by the singed 

 mutation was not discovered until after the singed- stock had been 

 discarded, so the eggs of singed- females were not examined. 



yaliiation of singed. 



From the description of the singed character it will be understood 

 that singed is very favorable for the purpose of classification, and since 

 the alteration is visible in every part of the body it should be exceptio- 

 nally useful for the study of gynandromorphs, even more useful than 

 forked, wMch is also one of the best characters for this purpose. The 

 general usefulness of singed is somewhat restricted by the fact that its 

 locus is very close to that of cut, which is one of the best sex -linked 

 characters for general work. In linkage work cut and singed are used 

 as alternates; and the data obtained with singed are combined with 

 those for cut by use of the known difference in distance. The singed 

 flies are of fair viability: and the males have excellent fertility in 

 striking- contrast to the females, which are absolutelv sterile. 



3. Forked». 



The singed mutation was. when first observed, supposed to be 

 allelomorphic to forked. The linkage tests proved that the new cha- 

 racter was due to an independent sex-linked recessive gene: and it was 



