production of Dolly the Sheep and also Megan and Morag, the two sheep that led to the production of Dolly, demonstrated that viable sheep can be produced by nuclear transfer from a variety of somatic cell types which have been cultured in vitro. Polly and Molly represented the further step in which somatic cells were cultured in vitro, just as in the case with the previous sheep. However, in this case they were transfected with foreign DNA, and the transfected cells which stably integrated this new piece of genetic information were selected. The nuclei of these somatic cells was then transferred into an empty oocyte, as in the procedure of nuclear transfer, and this was used to produce several transgenic animals. A cell type PDFF was used. PDFF5 would produce male animals and were not transduced. Cell type PDFF2 produced female animals and were transduced. Of the gestations that occurred, three PDFF2 animals were born, two of which survived birth, 7LL8 and 7LL12. These animals were transfected but contained a marker gene not the cloned gene of interest. These were named "Holly" and "Olly". Two more subsets of female-producing PDFF2 cells, PDFF2-12 and PDFF2-13, also produced animals which had the cell of interest together with the marker. Of these lambs, 7LL12, 7LL15, and 7LL13 were born alive and healthy. Two of these were named Polly and Molly. Transgene The transgene that was inserted in the donor somatic cells was designed to express the human clotting factor IX protein in the milk of sheep. This protein plays an essential role in blood coagulation, and deficiency leads to the disease haemophilia B of which treatment requires intravenous infusion of factor IX. The production of this protein in livestock milk, a process known as pharming, would provide a source of this therapeutic protein that would reduce the cost and also would be free of potential infectious risk associated with the current source of this protein (human blood). References 1997 animal births Cloning Cloned sheep Vertebrate developmental biology Cell biology Stem cells Biotechnology Individual animals in the United Kingdom