PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 6 NOVEMBER 15. 1920 Number 11 
HOMOLOGOUS GENES AND LINEAR LINKAGE IN DROSOPHILA 
VIRILIS 
By AIvExandkr WkinsTEin 
Garrison-on-Hudson, New York 
Communicated by T. H. Morgan, September 30, 1920 
Various species of Drosophila have produced mutations resembling in 
somatic appearance and in genetic behavior mutations in D. melano- 
gaster.^ In Sturtevant's case, involving notch in D. funebris, the resem- 
blances to the notch of D. melanogaster are so numerous that it seems 
extremely probable that the two factors are similar genes in homologous 
loci. In the other cases, however, the similarities are not sufficient to 
substantiate such a conclusion. 
Unfortunately, in all these instances, proof that the factors would act 
as allelomorphs if brought together is unavailable because the species 
studied do not hybridize with each other. However, even without data 
from hybridization, the homology of factors or of chromosomes in different 
species might still be detected if it were possible to demonstrate series of 
linked genes of which the similarly placed members have similar somatic 
effects. Metz has suggested that the yellow and forked genes in D. virilis 
are homologous with the similarly named genes in D. melanogaster. This 
identification, necessarily doubtful because only two factors were involved 
in each series, was rendered still more questionable by the discovery in 
D. melanogaster of singed (by Mohr) and inflated (by Weinstein^). The 
location of these factors is shown in figure IC. Inflated resembles vesic- 
ulated; and if the two factors were considered homologous, it would 
be possible (by turning the virilis chromosome round) to homologize 
forked in virilis with singed in melanogaster. Singed resembles forked 
in its bristles, but in addition in singed flies the hairs are affected and the 
females are sterile. The resemblance, therefore, is not so good as that 
between the two forked characters; still the differences between forked 
in virilis and singed in melanogaster might be due to modifying factors, or 
the two genes might be multiple allelomorphs. While, therefore, the 
identification of forked and vesiculated with singed and inflated is not so 
