Cases of mimic mutations ami secondary mutations in the X-chromosome ^cc. 3 



is also indebted to Dr. C. B. Bridges, who was kind enougli to correct 

 the English text, and from whom he obtained a corrected map of the 

 first chromosome^). 



2. Singed. 



The occurence of singed. 



In an experiment whicli was made in order to locate an autosomal 

 lethal that had arisen in the vestigial stock, a wild-type male with the 

 lethal-) and the vestigial gene in one of its Il-cliromosomes and the 

 gene for purple in the other was crossed to four females liomozygous 

 for the following recessive genes in the second chromosome: black purple 

 vestigial arc and speck. The expectation was that half of the Fi flies 

 would be purple and the other lialf vestigial, which was tlie case. But 

 it was observed in tlie first days count (Culture 558, Oct. 5, 1918j that 

 a few of the males showed a peculiar form of the large bristles upon 

 the head and the thorax. Instead of being long, slender and tapere'd 

 they w^ere shortened and curled as though singed by heat, not unlike 

 the recessive sex-linked character forked (f, bristles; at 56.5). The 

 final result of the counts was 41 purple and 44 vestigial females; 

 39 purple and 52 vestig^ial males. Of the purple males 4, and of the 

 vestigial males 7 were "'singed". 



The fact that only males exhibited this peculiar bristle character 

 indicated that it was recessive and sex -linked; and the number of 

 affected males made it probable that one of the females used in the 

 cross had been heterozygous for the gene in question. That the males 

 which carried the new character were derived from the black purple 

 vestigial arc speck ("5-ple") females w^as conclusively proven by back- 

 crossing one of the singed males to 5-ple females from stock. The 

 purple singed male tested gave 28 5-ple and 28 purple sons and 

 daughters (601, Oct. 17, 1918). One of the heterozygous females ob- 

 tained in this cross gave when outcrossed 113 females, 46 not-singed 

 and 37 singed males, thus proving that the character, like the old forked, 

 was recessive and sex-linked (680, Oct. 29, 1918). 



It was assumed that we were dealing with a reappearence through a 

 new mutation of the old character forked or of an allelomorph thereof 



^) This map has since been published in Proc. Natl. Acad. Sei., Febr. 1921. 

 *) Preliminary data indicate that this lethal gene is located in the II chromo- 

 some about .30 units to the left of vestigial, or at about 35 to the right of Star. 



1* 



