On July 5, 1996, the Roslin Institute in Scotland became the setting for a historic event with the birth of Dolly, the first sheep cloned from an adult cell. This scientific breakthrough, led by researchers Ian Wilmut and Keith Campbell, remained secret until February 1997, when it was revealed to the scientific community through the journal Nature.
Until Dolly’s birth, biology held that differentiated animal cells could not be reprogrammed to create a new organism. Dolly challenged this fundamental belief, demonstrating that adult cells still retain the ability to generate a complete being.
The process of cloning the sheep Dolly: nuclear transfer
The experiment used somatic cell nuclear transfer. Scientists extracted cells from the mammary glands of a Finn Dorset sheep, which were placed in a nutrient-deprived culture to induce a state of inactivity. Simultaneously, an unfertilized egg was obtained from a Blackface sheep.
The egg’s nucleus was removed through a process called enucleation, allowing the mammary cell nucleus to fuse with the empty egg. This fusion was facilitated by electric pulses that not only joined the cells but also mimicked the natural fertilization process, initiating the egg’s mitotic division.
A week of careful development in the laboratory allowed the fused egg to transform into a blastocyst-stage embryo, ready for implantation.
The experiment’s success rate was extremely low. Of the initial 277 fusions, only 29 embryos developed adequately and were implanted in Blackface sheep. Finally, only one pregnancy came to term, resulting in the birth of Dolly.
Dolly, originally identified as “6LL3”, was born with the same genetic profile as the Finn Dorset sheep, confirming that the recipient egg did not contribute genetically.
She lived at the Roslin Institute and had six offspring, but her health declined prematurely. In 2003, at six and a half years old, she was euthanized due to a lung tumor.
