Vpiy. 6, 1920 
GENETICS: A. WEINSTEIN 
635 
sterile. It ivS, of course, possible to determine the crossing over value of 
each gene with the nearest other factor and to compare the distances 
thus obtained. But such an experiment is necessarily inconclusive because 
variations in linkage caused by other genetic factors are difficult or 
impossible to eliminate unless the loci to be compared are followed in 
the same cross. 
Castle's prediction can, however, be disproved in another way, because 
there is evidence that rugose and glazed are allelomorphs. This is indi- 
cated by the similarity of their linkage relations (so far as tested) and of 
their somatic effects. Rugose dominates glazed, but this cannot be con- 
sidered evidence of allelomorphism because rugose females, and hence 
rugose-glazed hybrid females, are wild-type in appearance. (As the 
factors are sex-linked there are, of course, no males carrying both together.) 
However, I have found that glazed females are almost invariably sterile. 
(Out of 146 females tested in my experiments, either singly or in mass 
cultures, only two produced offspring.) The sterility of glazed, while it 
is recessive to wild- type fertility, is dominant to the fertility of rugose, so 
that rugose-glazed hybrid females are sterile. This suggests strongly that 
the rugose and glazed genes are allelomorphic ; and the evidence is 
strengthened by the behavior of a third mutant gene, wax, which in 
its somatic effects resembles rugose and glazed (though it is more extreme) 
and is, like them, sex-limited. Wax females, I have found, are also 
sterile. (Of 89 tested in my experiments, all but two failed to give 
offspring.) Wax eye is recessive to wild-type and to rugose, and the 
sterility of wax is recessive to the fertility of wild-type, but dominant to 
the fertility of rugose. (None of the 84 rugose- wax females tested in my 
experiments produced offspring.) Wax also, therefore, seems to be 
allelomorphic to rugose, and this is confirmed by the fact that glazed 
and wax behave as allelomorphs when crossed : the hybrid is intermediate 
and, as would be expected, sterile. (None of the 106 tested produced 
offspring.)^ 
Since the evidence indicates that rugose and glazed are allelomorphs, 
the amount of crossing over between them, if it could be directly deter- 
mined, would be not about 4 or 5 per cent (as Castle predicted), but 0. 
Coincidence in Drosophila virilis. — While the data in Drosophila virilis 
are not sufficiently extensive for any detailed considerations of coincidence, 
they indicate, as far as they go, that the coincidence of various regions 
resembles that of the corresponding regions of the X chromosome in D. 
melanogaster. 
The values of table 6, because of the smallness of the figures and 
the uncertainty of vesiculated as a diagnostic character, are subject to 
large error; but they all agree in indicating that coincidence first 
