Cloning (somatic cell nuclear transfer) in avian species has proven unachievable due to the physical structure of the avian oocyte. Here, the sexual differentiation of primordial germ cells with genetic sex ZZ (ZZ PGCs) was investigated in female germline chimeric chicken hosts with the aim to produce uniparental offspring. ZZ PGCs were expanded in culture and transplanted into the same and opposite sex chicken embryos which were partially sterilized using irradiation. All tested chimeric roosters (ZZ/ZZ) showed germline transmission with transmission rates of 3.2%-91.4%. Unexpectedly, functional oogenesis of chicken ZZ PGCs was found in three chimeric hens, resulting in a transmission rate of 2.3%-27.8%. Matings were conducted between the germline chimeras (ZZ/ZZ and ZZ/ZW) which derived from the same ZZ PGCs line. Paternal uniparental chicken offspring were obtained with a transmission rate up to 28.4% and as expected, all uniparental offspring were phenotypic male (ZZ). Genotype analysis of uniparental offsprings was performed using 13 microsatellite markers. The genotype profile showed that uniparental offspring were 100% genetically identical to the donor ZZ PGC line, shared 69.2%-88.5% identity with the donor bird. Homozygosity of the tested birds varied from 61.5% to 84.6%, which was higher than the donor bird (38.5%). These results demonstrate that male avian ZZ PGCs can differentiate into functional ova in an ovary, and uniparental avian clones are possible. This technology suggests novel approaches for generating genetically similar flocks of birds and for the conservation of avian genetic resources.

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