One potential impact of interest is perturbation of the natural sex ratio, and recent studies have shown that changes in the proportion of male Talazoparib gametocytes taken up by feeding mosquitoes can affect transmission. Rodent parasite studies strongly implicate sex ratio as an indicator of fitness in P. chabaudi. Studies of P. falciparum in vivo have suggested that drug treatment may differentially affect the half-life of male and female gametocytes, and therefore may affect the transmission success of the parasite. Currently, the standard method for quantifying the P. falciparum gametocyte sex ratio remains the identification of male and female gametocytes by light microscopy, using five discriminatory morphological characters. Individual P. falciparum gametocytes from in vitro cultures have been sexed with alternative methods at low densities, including electron microscopy, in situ hybridization, immunoelectron microscopy and immunofluorescent antibody test. However, these methods are laborious, and hitherto have only been applicable to small numbers of specially prepared gametocytes, and have thus not been used to derive reliable estimates of the gametocyte sex ratio in vitro. Further, all studies to date have estimated sex ratios in preparations of mature stageIV/stageV gametocytes only, as sexdistinguishing morphological characteristics are absent in immature stages. Discrimination between the gametocyte sexes by IFAT has relied on two relatively well characterised sexual stage proteins, Pfg377 used to identify female gametocytes and a-tubulin II which has been used to identify male gametocytes. a-tubulin II has been described as a gametocyte-specific, male-specific protein in P. falciparum. However recent studies in rodent malaria parasites have demonstrated transcription and expression of the P. berghei homologue of this protein in both asexual parasites and female gametocytes in infected mice. In P. falciparum, there is some in vitro evidence of expression of the a-tubulin II protein in asexual parasites, although these authors analysed expression of this protein from bulk cultures and so could not rule out the presence of some young parasites committed to sexual development. However, Khan et al. were able to use a-tubulin II in transfected P. berghei parasites as a marker to separate male from female gametocytes using fluorescent flow cytometry, suggesting much higher expression levels are found in male compared to female gametocytes, at least in this rodent parasite. The utility of this protein as a potential male-specific probe in P. falciparum thus remains unclear. A strategy for discriminating P. falciparum gametocyte sexes based on differential antibody staining by IFAT was deployed to examine sex ratios at all stages of gametocyte development in vitro.