M factors, which determine maleness in Musca domestica, were found on the s
econd, third, fourth and fifth linkage groups in housefly populations of Tu
rkey. As in European populations, the male-determining factor was more freq
uently located on linkage group III (M-III). Some males homozygous or doubl
e heterozygous for M factors were identified. Deviations from a 1:1 sex rat
io in favour of males, as well as mosaics for somatic marker mutations and
sexual mosaics (gynandromorphs), were also observed. The results reveal an
extensive polymorphism in the sex-determining system.