A NEW SECOND CHROMOSOME EYE COLOUR GENE 393 

TABLE 2. 
Coupling test. P, mating, plexus brown OX wild-type &: B.'C.,; Eı 
wild type? X plexus brown  . 








| Jan. 25. 1921 | non-cross-overs | cross-overs 
| pe bw) pe bw 
ary OES. AU ie; 
324 AS D De) hae 
326 PS 384. Al 1 
327 | 40 13 | 0 1 
i 328 EM 29 29 ng ee 
(ee Pie a PL ar 0 
; Total | Tor 41 | 5 716 
TABLE 3. 
Triple recessive test. P, mating, arc plexus brown & X wild type 3: 
B. C., F, wild type © X arc plexus brown d. 






| | | | 
| Feb. 8. 1921 2 | 2 - 
+ a px bw a px bw | a px bw 
| 334 1178 32,588 as ER EB 5 
| 335 - 82 63 1 RUES 3 
| 336 82 BI Al 0 6 7 
| 337 Wera TS AE DS A 4 1 7 
| 338 79 BETA PP DE 2 
| 339 BH TORRES QE AA LUS 0 | 
340 94 iy eo tie 2 3 3 | 
Total CU 7.5635 AA ig 12: <a O77 «| 
As seen from tables 1—38, 108 cross-overs between plexus and 
brown were obtained in a total of 2,833 flies. This means that there 
is a distance of 3, units between the two genes mentioned. In the 
arc plexus brown test no flies were obtained which were arc 
brown or plexus. The locus of plexus is accordingly between the loci 
of the two others. Since are and plexus according to the most recent 
data are mapped as having their loci at 97,5 and 98,3 respectively, the 
locus of brown is found to be at 102,1. 
The eye colour of newly hatched brown individuals is a pure, 
transparent brown, lighter than the wild type red. This colour rapidly 
