YoL. 6, 1920 
GENETICS: A. WEINSTEIN 
633 
These results demonstrate, despite the great differential mortality in 
many broods, that the hairy locus is to the left of magenta; because 
whenever there is crossing over between hairy and magenta, forked goes 
with the linked gene in the magenta locus, and vesiculated (except for 
occasional double crossing over) goes with the linked gene in the hairy 
locus. If we consider only those broods in which there is no marked 
differential mortality (A1539 and B), we obtain the same result. 
Linear Linkage in Drosophila virilis. — The data on the linkage of yellow, 
crossveinless, and vesiculated, and of hairy, magenta, and forked, are of 
interest because they demonstrate that in each case the three genes are 
in strictly linear order, the longest distance being the exact sum of the 
TABLE 5 
A. Offspring of — Female 
h m 
MALES 
CULTURE NO. 
FEMALES 
0 
1 
2 
1,2 
TOTALS 
y 
h m 
y h m 
+ 
y m 
h 
m 
1369 
89 
35 
29 
23 
18 
1 
4 
1 
111 
B. Offspring of - Female 
m 
CULTURE NO. 
MALES 
FEMALES 
h 
m 
h m 
TOTAL 
1529 
71 
22 ■ 
7 
1 
30 
two shorter distances. Hitherto the only species for which such data 
have been presented has been D. melanogaster, in which, as Sturtevant, 
Bridges, and Morgan,^ and Muller^ have shown by reference to the results 
of critical tests, the arrangement of the genes is exactly linear. As a 
result of criticisms by these authors, Castle^ has withdrawn his objections 
to the theory of linear linkage. In D. virilis, however, there have been 
hitherto no decisive data published. Metz's results, while they agree 
so far as they go with those in melanogaster, do not go far enough to give a 
decisive proof of linear arrangement. In the only case (that of hairy, 
magenta, and forked) in which the factors with which he worked were 
sufficiently close together to make a crucial test possible, he failed to make 
the necessary cross. 
