392 GEORG H. M. WAALER 
triple recessive stock see BrivGes, 1919) for the two second chromosome 
recessives dachs (legs, d, at 29,0) and black (body colour, bl, at 46,5) 
in order to determine the linkage relation of brown to these two 
previously known loci. In a total of 2578 flies there was found 
a crossing-over percentage of 45,7 between brown and black and 46,7 
between brown and dachs. 
This result raised doubts as to the correctness of the classifica- 
tion in the Star Dichaete back-cross, as there was a discrepancy 
between the linkage values obtained in the two tests. A brown black 
male back-cross, i. e. homozygous brown black female X heterozygous 
male, was accordingly carried out. Since there is no crossing-over 
in the male, this cross would show conclusively whether or not the 
gene was located in the second chromosome. The result was: 
bw bl + bl bw 
70 53 0 0 
which proved that the locus of brown was in the second chromosome. 
The black brown linkage value obtained above (45,7 % ), seen in 
connection with the values obtained in the Star Dichaete female back- 
cross, made it appear likely that the locus of brown was at the right 
end of the second chromosome, and in a final experiment it was de- 
cided to determine the linkage relation of brown to genes which had 
their loci in this part of the chromosome. As such were used plexus 
(venation, px, at 98,3) and are (wing, a, at 97,5). 
TABLE/ 1. 
Repulsion test. P; mating, plexus 2 X brown J; B. C., F, wild type © 
plexus brown 6. 
Nov. 27. 1920 non-cross-overs cross-overs 
px bw + px bw | 
280 122 149 4 6 
281 103 113 > 4 
282 98 a Niro 2 
283 95 110 4 | 
286 72 101 | 7 
287 56 71 3 0 
325 29 23 2 0 

Total 575 664 25 23 
“ri 
