Polly and Molly (born 1997), two ewes, were the first mammals to have been successfully cloned from an adult somatic cell and to be transgenic animals at the same time.
The creation of Polly and Molly built on the somatic nuclear transfer experiments that led to the cloning of Dolly the Sheep.
The gene chosen was a therapeutic protein to demonstrate the potential of such recombinant DNA technology combined with animal cloning.
[3] Prior to the production of Polly and Molly, the only demonstrated way to make a transgenic animal was by microinjection of DNA into the pronuclei of fertilized oocytes (eggs).
Polly and Molly represented the further step in which somatic cells were cultured in vitro, just as in the case with the previous sheep.
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.