OF MUTANT CHARACTERS. 257 



determination of the locus was not made, though this would have been 

 done had the stock not died out because of its low productivity and 

 sterility. 



CONFLUENT VIRILIS. 



Metz (C. W. Metz, Journ. Gen., 1916, p. 591) found in the species 

 Drosophila virilis a mutation which was a very striking counterpart 

 of confluent of D. melanogaster in all respects, save that it was neither 

 so sterile nor so non-productive. The character of the venation was 

 practically the same in the two cases, though in confluent D. melano- 

 gaster the venation may liave been a trifle thicker and knottier in the 

 affected regions. Confluent D. virilis was a dominant which gave 1 : 1 

 ratios upon inbreeding, precisely as did confluent D. melanogaster. 



There is no doubt of the completely lethal effect of confluent virilis 

 when homozygous, and in confluent melanogaster the only indication 

 that an occasional homozygote may survive is the fact that 1 out of 10 

 of the flies successfully tested. by Metz gave a 27 :0 ratio of confluent 

 to wild-type, instead of the 18 : 9 ratio expected. The other 9 flies 

 tested by Metz were all heterozygous, as had been all those worked 

 with by Bridges. It is possible that this 27 : ratio was the result of 

 a balanced lethal condition such as obtains in truncate, snub, beaded, 

 and other stocks. 



The fact that several of the mutations secured in D. virilis (or other 

 species) seem parallel in appearance and inheritance with the known 

 mutants of D. melanogaster is of great interest as an indication of the 

 basic similarity of the two systems of genetic materials. 



FRINGED (f r ). 



(Text-figure 82.) 



ORIGIN OF FRINGED. 



In the F 2 from a cross of the sex-linked wing-character ''jaunty I" 

 to wild (culture 1042, January 20, 1915), Bridges found that about a 

 quarter of the flies of both sexes were showing an irregular distribu- 

 tion of the hairs on the marginal vein of the wing. The margin showed 

 spots entirely denuded of hairs or with only weak hairs, while the 

 remaining hairs were frayed and irregular in directions. The wings 

 also were slightly smaller, a trifle discolored, and occasionally divergent. 



CHROMOSOME CARRYING FRINGED. 



One of the "fringed" males was out-crossed to a black female and 

 produced in F 2 the typical 2:1:1:0 ratio that showed that the locus 

 of fringed is in the second chromosome (table 105). From the F 2 

 black and fringed inbred a stock of black fringed was obtained in F 4 . 



A similar attempt to obtain a fringed speck double-recessive stock 

 from the F 2 of the cross of fringed by speck (table 106) failed entirely. 



