How did electrical pulses help create Dolly the sheep?

In the creation of Dolly the sheep, electrical pulses were used to facilitate the fusion of a donor mammary gland cell with an unfertilized egg cell that had been stripped of its own nucleus.1

By applying these electrical pulses, researchers at the Roslin Institute successfully transferred the nucleus of the adult mammary cell into the host egg cell. This fusion process was a critical step in somatic cell nuclear transfer (SCNT), as it allowed the donor nucleus to be integrated into the egg's cytoplasm, where it could then be reprogrammed to begin the process of cell division and embryonic development.12

Before this fusion could occur, the donor mammary cell had to be induced into a quiescent, or dormant, stage by withholding nutrients, which ensured the nucleus would be receptive to the environment of the host egg. Once fused via the electrical pulses, the resulting reconstructed embryos were implanted into surrogate mothers, eventually leading to the birth of Dolly.13