In this new study, detailed this week in the journal Nature Methods, Hufnagel and colleagues recorded the movements of every cell nucleus in the embryo not only during the later developmental stages, but also throughout the first three hours of the embryo's life, when nuclei divide very rapidly.
Sir Ian and his team fused the genetic information from an adult sheep cell nucleus with an egg cell to form an embryo that developed into a genetically identical copy of the original adult.
Reproductive cloning, which created Dolly the sheep in 1997, involves transferring the nucleus of an adult cell into an egg, giving the resulting embryo a full set of genes without the normal sperm-meets-egg fertilisation step.