Under control conditions, fru^M heterozygotes and fru^M/fru^4-40 transheterozygotes do not show significant changes in mitotic index in the female and male adult posterior midgut, as compared to controls.

fru^M/+ adult females have the male-specific ventrolateral protocerebrum projection neuron 1, which is not seen in control females; there is no effect on its presence in the male.

fru^M females show a significant increase in the number of pIP10, dPR1, vPR1, vPR6, aDT2/mAL, aSP1 and aSP2 neuronal cells per hemisphere compared to fru[+] females. The aDT2, aSP4 and vAB3 neurons show an apparently complete transformation to male-like morphology in these females.

In fru^M/fru^4-40 females the post-embryonic Ilp7 neurons in the posterior adult ventral nerve cord are partially masculinised; the ventral cluster of female-specific Ilp7 neurons are still present but, as in males, the shared dorsal cluster neurons express serotonin.

XX animals carrying fru^M show transformation of their brain neuropil morphology to that normally seen males. The transformation is incomplete, as the "male-enlarged region" (MER) volume is enlarged 25 +/- 5% in the brains of fru^M XX animals compared to in control females (whereas the MER is enlarged 38 +/- 6% in control males compared to control females).

In fru^M mutant males, dsx-pC1, dsx-pC2 and dsx-pC3 neuronal numbers are significantly reduced compared with wild-type. A substantial reduction in the density of axons is observed in the cervical connection and in the contralateral connections in the prothoracic ganglia. There is no reduction in the dsx-SN, dsx-TN1 or dsx-TN2 cluster.

dsx-expressing neurons in females expressing fru^M are not significant different from those in wildtype females.

P1 neurons are present in XY fru^M animals and not in XX fru^M animals (these neurons are normally only found in male brains in the wild type).

fru^M females exhibit male courtship behaviour and certain virgin and mated female behaviours are suppressed (copulation and egg-laying, respectively). These females are not induced to lay eggs, as in wild-type.

The normally male specific 'muscle of lawrence' is ectopically present in fru^M/fru^4-40 females. fru^M/fru^4-40 males exhibit normal levels of courtship behaviour towards females. fru^M/fru^4-40 show a significant competitive advantage over wild-type control males in competition for copulation with a wild-type virgin female. This may be mainly due to a significant decrease in courtship latency seen in these males. They do not show any increase in courtship of other males compared to wild-type and do not form into mating chains. Less than 25% of fru^M/fru^4-40 females are fertile. In mating assays in which a single virgin fru^M/fru^4-40 female is paired with a wild-type male, less than 16% of these females copulate. fru^M/fru^4-40 females court wild-type females, with courtship indices over 40% in single-pair assays. They also form courtship chains with other fru^M/fru^4-40females (chaining indices >40%). These females perform all steps in the male courtship ritual apart from copulation, which is anatomically impossible, and abdominal bending in attempt to copulate, which may be inhibited by the much larger abdomen of females. However, the proportion of time spent in different parts of the courtship ritual differs form control (fru^C/fru^4-40) males: they spend significantly more time tapping and less time licking, overall courting time is reduced but initiation of courtship is just as rapid. Unlike control females, these females also court males. Courtship of males by fru^M/fru^4-40 females is significantly enhanced if the males are tra^Scer\UAS.cFa; Scer\GAL4^oeC.

The sexual dimorphism of the volumes of the DA1, VA1v and VL2a antennal glomeruli is eliminated in fru^M mutant animals. fru^M mutant females court tra^Scer\UAS.cFa; Scer\GAL4^oeC males.

Females court other females and are nearly sterile.