GENETICS × TECHNOLOGY
Dolly the Sheep, the First Cloned Mammal
1996 CE
History · Contemporary · Holocene · Meghalayan
Dolly was a ewe born on 5 July 1996 at the Roslin Institute, near Edinburgh, and the first mammal grown from a cell taken from an adult body. The method, somatic cell nuclear transfer, strips an unfertilised egg of its own nucleus and puts in its place the nucleus of a body cell, here a cultured cell from a mammary gland; the reconstructed egg then develops as an embryo. The question behind the attempt was old. A body cell reads only the part of its genome that its tissue requires, and differentiation was long held to alter the rest beyond recovery. A lamb carried to term from such a nucleus showed that no irreversible change had occurred, and that an egg can bring the whole programme back to its starting state. The yield was very low, one live birth for 277 attempts, and the result rested on an earlier finding by the same group, that donor cells first driven into quiescence support development. Nature published the paper on 27 February 1997, seven months after the birth.
Why it matters
The birth answered a question that hangs over every cell of a body: a nucleus that has specialised still holds a complete and usable genome, and an egg can take it back to the beginning. From that answer came the search for factors able to perform the same reversal without an egg, which is the basis of nuclear reprogramming and of the regenerative medicine built on it, together with new means of breeding livestock and of keeping threatened species. The procedure has stayed inefficient, and that inefficiency, with the losses it imposes on the animals carrying the pregnancies, remains the first argument raised against any use in humans.
Dating & uncertainty
Dolly was born on 5 July 1996 and the paper describing her appeared on 27 February 1997, so the same event is dated to either year. The measurement is not in doubt; what the choice changes is which act is being dated, the laboratory's or the journal's, and the birth is what is dated here. A second dispute, about her body rather than her year, ran much longer: osteoarthritis in a knee suggested that a clone might age early, but thirteen cloned sheep aged seven to nine years, four of them from the cell line that produced her, were later examined and found free of any clear degenerative joint disease beyond mild cases.
Sources
- Wilmut et al. (1997), Nature · Viable offspring derived from fetal and adult mammalian cellsdoi:10.1038/385810a0
- Edwards et al. (2003), American Journal of Reproductive Immunology · Cloning Adult Farm Animals: A Review of the Possibilities and Problems Associated with Somatic Cell Nuclear Transferdoi:10.1034/j.1600-0897.2003.00064.x
- Sinclair et al. (2016), Nature Communications · Healthy ageing of cloned sheepdoi:10.1038/ncomms12359
- Alberio et al. (2021), Reproduction · 25th ANNIVERSARY OF CLONING BY SOMATIC-CELL NUCLEAR TRANSFER: Nuclear transfer and the development of genetically modified/gene edited livestockdoi:10.1530/rep-21-0078
Our species’ history as one day
23:59:518.2 s before midnight
if the 315,000 years of Homo sapiens were compressed into a single day