Vol,. 7, 1921 
GENETICS: A. H. STURTEVANT 
235 
A CASE OF REARRANGEMENT OF GENES IN DROSOPHILA 1 
By A. H. Sturtsvant 
Columbia University, New York City 
Communicated by T. H. Morgan, May 28, 1921 
Seven mutant genes of Drosophila simulans have been shown to be 
allelomorphic to previously known mutant genes of D. melanogaster. 2 
Five of these lie in the X-chromosome, and a study of their linkage re- 
lations was shown to indicate that the sequence of the five loci concerned 
is the same in both species, and that the percentages of crossing over in 
comparable regions, while not indentical, is still not very different. The 
other two allelomorphic mutant genes, scarlet and peach, lie about 3 units 
apart in the third chromosome of melanogaster; in simulans they lie in 
the same chromosome (which is thus identified as the third one), but 
they were found to be at least 45 units apart. 
More recently two more mutant genes of simulans that lie in the third 
chromosome have been studied. One of these, dachs, 3 lies to the left 
of scarlet; the other, deltoid, 4 lies between scarlet and peach. The latter, 
since it makes possible the detection of a portion of the double crossovers, 
has resulted in a more accurate determination of the scarlet peach dis- 
tance. The map based on the linkage relations of these four loci (not 
corrected for unobservable double crossing over) is shown in figure 1. 
Both of the new mutant types, dachs and deltoid, resemble previously 
known mutant types in D. melanogaster. Dachs in melanogaster lies 
in the second chromosome; it is accordingly not surprising that tests 
have shown it not to be allelomorphic to dachs simulans. Deltoid re- 
sembles delta melanogaster. Since both genes are dominant, the usual 
test of allelomorphism could not be applied; but each has also a recessive 
lethal effect, and crosses of delta melanogaster by deltoid simulans have 
shown that the hybrids that receive both mutant genes do not develop. 
It follows that the two genes are allelomorphic. The map of the melano- 
gaster third chromosome, including the known ends and the three loci 
occupied by parallel mutations, is shown in figure 2. 5 
A comparison of figures 1 and 2 shows that the three identical loci are 
not in the same sequence in the two species. 
Mr. D. E. Lancefield has obtained evidence suggesting a similar re- 
arrangement of genes in the X-chromosome of D. obscura. His results 
were obtained before those here reported, but are not yet published. 
Since D. obscura has not yet been crossed with any other species, the 
evidence for identity of loci is not conclusive in this case. 
The only analogous case so far reported appears to be that briefly de- 
scribed by Bridges 6 under the name of "vermilion duplication." In 
