IQ . Mohr. 



When the data from Table 2 and 3 are taken together we get 

 43 recombinations of cut and singed in a total of 4714 males. This 

 gives a distance of 0.9 units. The cut gene is located at 20. o. so the 

 singed locus is at 20.9. 



The combined action of singed and forked. 



The fact that singed, like the sex-linked mutant character forked, 

 caused a very marked alteration of the bristles made it desirable to 

 determine whether a simultaneous action of these two genes in double 

 recessive singed forked flies would give a more extreme alteration of 

 the macroch;Tpt:v. 



Singed males were crossed to inflated forked Bar females (inflated, 

 in, wing, around 54; Bar, B, eye, at 57.0), and the Fi Bar daughters, were 

 crossed to inflated forked Bar males (906, Dec. 11, 1918). The singed 

 inflated Bar males resulting from this cross are known to be forked 

 also, since the locus of forked (at 56.6) is between those of inflated 

 and Bar and tliis distance is so short that double crossing-over is excluded. 



Contrary to what might have been expected, it was found that 

 these double recessive singed forked males looked entirely like ordinary 

 singed individuals. The forked character had no detectable modif\ing 

 effect upon the action of the singed gene. 



The reappearance of the singed character as a result of a new 



mutation, singed-. 



In a back-cross of a Notch 8 female heterozygous for broad 

 echinus and ruby (broad, br, wing, at 0.6) to broad echinus ruby males 

 a stngle broad echinus ruby male occured which was also singed (1778, 

 Nov. 5, 1919). The culture gave 220 females and 102 males. Of the 

 latter 99 were broad echinus ruby, 1 echinus ruby and 2 broad echinus. 

 The 2 : 1 sex ratio is due to the lethal action of the Notch 8 mutation, 

 this mutation being a deficiency involving most of the section between 

 broad and echinus (Mohr '19). 



The singed character of the single male looked entirely like 

 ordinary singed. In order to test whether this character represented 

 a reappearance of the singed gene or an allelomorph thereof, the male 

 was crossed to females from an unrelated stock, and his daughters, 

 heterozygous for "'singed-" were tested by males from the old singed 

 stock (1855, Dec. 2, 1919). Half of the daughters of the females tested 



