258 



THE SECOND-CHROMOSOME GROUP 



LOCUS OF FRINGED. 



The black fringed stock, in combination with the recently mapped 

 dominant star, offered a means of locating the position of fringed. 

 A three-locus back-cross was started by mating a black fringed male 

 to a star female and back-crossing the Fi star females by black fringed 

 males. The three back-cross cultures (table 107) gave a total of 496 

 flies, of which 153 were non-cross-overs, 133 single cross-overs between 

 star and black, 141 single cross-overs between black and fringed, and 



Text-figure 82. — Fringed wing-margin. 



70 were double cross-overs. The black fringed cross-over value was 

 42.5, which places fringed at practically the same locus as arc, which 

 gave 42.6 as the black arc cross-over value. 



To determine the locus more closely than this would require fringed- 

 speck or fringed arc back-crosses, which have not been made. The 

 only cross-over data on fringed are the values calculated from the star 

 black fringed back-cross above, viz, S'b = 40.9, bfr = 42.5, 8% = 55.2. 



