the cells will proliferate rapidly and maintain their pgc phenotype that the pgcs can be passaged at daily or 2 day intervals that the pgcs will colonize the germline but not somatic tissues after at least 110 days in culture that viable offspring can be obtained from cells that have been in culture for 110 days that the pgcs can be genetically modified by transfection with a transgene and that the genetically modified pgcs can be isolated and propagated into a colony of genetically modified pgcs pursuant to this invention chicken pgc cell lines have been derived from blood taken from stage 16 h amp h embryos that have a large round morphology fig1 these cells are confirmed to be chicken pgcs by their morphology after long term culturing and their ability to yield pgc derived offspring in addition the pgc cultures express the germline specific genes dazl and cvh fig2 and the cvh protein is produced by the cells in culture fig3 pgcs in culture also express telomerase fig4 indicating that they have an immortal phenotype furthermore pgcs will give rise to embryonic germ eg cells in the appropriate culture conditions fig5 by analogy mouse and human pgcs will give rise to eg cells when treated in an analogous fashion mouse eg cells will contribute to somatic tissues and chicken eg cells also contribute to somatic tissues as indicated by black feather pigmentation in chimeras fig6 chicken pgcs have been genetically modified as indicated by southern analysis fig7 in a preferred embodiment the cx promoter is stably integrated into the genome of a pgc and is used to facilitate expression of the gene encoding aminoglycoside phosphotransferase aph which is also integrated into.