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 the genome of a pgc and is used to confer resistance to neomycin added to culture media in order to select pgcs that have been genetically modified two to five u03bcl of blood taken from the sinus terminalis of stage 15 17 h amp h embryos were incubated in 96 well plates.