Cloning (SCNT) in avian species has proven unachievable due to the physical structure of the avian oocyte. Here, the plasticity of sexual differentiation of male primordial germ cells (PGCs) was investigated in opposite sex chimeric chicken hosts with the aim of producing uniparent clones. Male (ZZ) PGCs were expanded in culture and transplanted into the same and opposite sex chicken host embryos which were partially sterilized using γ-irradiation. As expected, all (28/28) chimeric (ZZ) roosters showed germline transmission with transmission rates of 3.2- 91.4% as detected by feather color. Unexpectedly, functional oogenesis of male chicken PGCs was found in three chimeric (ZW) hens (3/27), resulting in transmission rates of 2.3- 27.8%. Matings were conducted between the male and female germline chimeras which derived from the same male PGC line. 20 uniparent chicken clones were obtained with a transmission rate up to 28.4% and as expected, all uniparent offspring were male (ZZ). A genotype analysis was performed on 6 offspring using 13 microsatellite markers. The genotype profile of these offspring showed that uniparent offspring were 100% genetically identical to the donor male PGC line, and shared 69.2-88.5% identity with the donor bird at the 13 loci. At the 13 loci, homozygosity of the tested birds varied from 61.5-84.6%, which was higher than that of the donor bird (38.5%). These results demonstrate that male avian PGCs can differentiate into functional ova in an ovary and uniparent avian clones are possible. Uniparent clones differ from SCNT clones as the mitochondrial DNA derives from the donor and not from the host. This technology suggests novel approaches for generating genetically similar flocks of birds and for the conservation of avian genetic resources. Forming uniparent clones in bird species could be useful in extreme cases of low populations size.