A SOMATIC MUTATION IN DHGSOPIIILA MMI.ANOGASTEH 



153 



through new mutation of the old singed gene or with an allelomorj)!! 

 thereof. Whctlier this was the case could be ascertained by mating 

 the new mutant to old singed individuals and by determining the 

 locus of the new recessive through linkage experiments. Both these 

 tests were carried out. 



Six females from (>. 2703, Table 1, were crossed to singed males 

 from the old singed stock. We know that half of the daughters in 

 this culture are heterozygous for the new mutant gene, since half of 

 their brothers showed the corresponding character. Some of the 

 females resulting from this mating are accordingly expected to mani- 

 fest a bristle and hair alteration, if the two ^enes are allelomorphic. 

 They will namely have the old singed gene in one X-chromosome and 

 the new allelomorph in the other. The culture gave 62 wild-type $$, 



TABLE 4. Pi; crossveinless cii^ $$ >< new singed (sn^)(^<^. B. C. 



(cu cP \ 

 A, X crossveinless cut^ çfj*. 



22 singed ??, 39 wildtype c^d" and 18 singed cTci' (C. 2724, July 14, 

 1922). The converse cross of a female heterozygous for the old 

 singed gene and in addition for the sex-linked recessive fused ifu, at 

 59,5, fused veins) X new singed males gave wild-type and sn females; 

 sn fu, sn and /« males, (C. 2758, Aug. 9, 1922). 



Thus it was clear that the two genes were allelomorphic. The 

 old singed-new singed compound (in the females) looked entirely 

 like both the old singed and the new singed character. It seemed 

 therefore probable that the two genes were identical. 



The result of the linkage tests is presented in Table 4. Females 

 homozygous for the recessive sex-linked mutant genes crossveinless 

 [cv, at 13,5; fifth crossvein lacking) and cut (c/", an allelomorph of 

 ct, cut wings, at 20,o) had been crossed to new singed males. Two 

 heterozygous daugthers were now back-crossed to cv ct^ males. As 



