GENETICS: W. E. CASTLE 
33 
with the linkage relations of eight sex-linked characters in Drosophila virilis, 
a species distinct from D. ampelophila, which has been so exhaustively studied 
by Morgan and his pupils. Of the eight characters studied by Metz, two 
agree morphologically and in their linkage relations with each other, with 
similar characters of D. ampelophila. The six others have no exact counter- 
part among the known mutations of D. ampelophila. The two characters in 
question are yellow body and forked bristles. Yellow body, in both species, 
lies at the extreme, 'zero' end of the linkage system. Forked, in both species 
lies at a distance of 40 or over from yellow. In D. virilis the distance is 
exactly 40, according to the observations of Metz; but in D. ampelophila, ac- 
cording to Morgan and Bridges, the distance is about 6 or 7 units greater. 
But inspection of figure 1 (p. 29) shows that this estimate is probably too 
TABLE 1 
GENES 
TOTALS 
CROSS-OVERS 
PERCENTAGE 
CROSS-OVERS 
308 
4 
1.3 
3,548 
621 
17.4 
3,049 
1,157 
38.0 
Yellow-liairy 
162 
65 
40.1 
3,781 
1,510 
40.0 
1,328 
591 
44.5 
Yellow-rugose 
1,060 
502 
47.3 
296 
55 
18.6 
Vesiculated-magenta 
2,799 
944 
33.7 
3,761 
1,395 
37.1 
Vesiculated-glazed 
877 
359 
42.1 
Vesicula ted- rugose 
1,696 
729 
42.9 
2,529 
95 
3.7 
Magenta-rugose 
824 
197 
23.9 
Hairy-forked 
162 
5 
3.1 
Forked-glazed 
749 
193 
25.7 
1,158 
321 
27.7 
high, since the wire joining white (TF) with forked {F) in the model is too long 
to harmonize fully with other linkage-values given by Morgan and Bridges, 
the wire being curved. The distance yellow-forked is not given by Morgan 
and Bridges but it evidently should be about one unit greater than the dis- 
tance, white-forked, which is given as 45.7. If this estimate of the distance 
is too high, as figure 1 indicates, then the distance yellow-forked is probably 
not very different in the two species of Drosophila and will be found to be not 
far from 40 in both. 
The linkage values found by Metz for the eight sex-linked genes of D. 
virilis have been gathered from his several tables, averaged and brought 
together in table 1 herewith. They form the basis of the reconstruction shown 
in figures 3 and 4. 
