was a ewe
– February 14
) that was the first animal
to be cloned
from an adult somatic cell
, using the process of nuclear transfer
. She was cloned by Ian Wilmut
, Keith Campbell
and colleagues at the Roslin Institute
. She was born on July 5
and she lived until the age of six, and was dubbed "the world's most famous sheep" by Scientific American
The cell used as the donor for the cloning of Dolly was taken from a mammary gland, and the production of a healthy clone therefore proved that a cell taken from a specific body part could recreate a whole individual. More specifically, the production of Dolly showed that mature differentiated somatic cells in an adult animal's body could under some circumstances revert back to an undifferentiated pluripotent form and then develop into any part of an animal. As Dolly was cloned from part of a mammary gland, she was named after the famously busty country western singer Dolly Parton.
This used the technique of Somatic cell nuclear transfer
, where the cell nucleus
from an adult cell is transferred into an unfertilized oocyte
(developing egg cell) that has had its nucleus removed. The hybrid cell is then stimulated to divide by an electric shock, and when it develops into a blastocyst
it is implanted in a surrogate mother.
In the previous year, the same team had produced cloned sheep from the embryonic cells, but this was not seen as a breakthrough since adult cloned animals had been produced from embryonic tissue as long ago as 1958, using cells from the frog Xenopus laevis.
Dolly was the first clone produced from a cell taken from an adult animal. However, this cloning process is still highly inefficient, with Dolly the only lamb that survived to adulthood from 277 attempts. She is also recognised as one of the major stepping stones in the development of modern biology. Wilmut, who led the team that created Dolly, announced in 2007 that the nuclear transfer technique may never be sufficiently efficient for use in humans.
Dolly lived for her entire life at the Roslin Institute. There she was bred with a Welsh Mountain ram
and produced six lambs in total. Her first lamb called Bonnie, was born in April 1998. The next year Dolly produced twin lambs Sally and Rosie, and she gave birth to triplets Lucy, Darcy and Cotton in the year after that. In the autumn of 2001, at the age of five, Dolly developed arthritis
and began to walk stiffly, but this was successfully treated with anti-inflammatory
On February 14
, Dolly was euthanised
because of a progressive lung disease. A Finn Dorset
such as Dolly has a life expectancy of around 11 to 12 years, but Dolly lived to be only six years of age. A post-mortem examination showed she had a form of lung cancer called Jaagsiekte
that is a fairly common disease of sheep and is caused by the retrovirus JSRV
. Roslin scientists stated that they did not think there was a connection with Dolly's being a clone, and that other sheep in the same flock had died of the same disease. Such lung diseases are a particular danger for sheep kept indoors, and Dolly had to sleep inside for security reasons.
However, some have speculated that a contributing factor to Dolly's death was that she could have been born with a genetic age of six years, the same age as the sheep from which she was cloned. One basis for this idea was the finding that Dolly's telomeres were short, which typically is a result of the aging process. However, the Roslin Institute have stated that intensive health screening did not reveal any abnormalities in Dolly that could have come from advanced aging.
After cloning was successfully demonstrated through the production of Dolly, many other large mammals have been cloned, including horses
. The attempt to clone argali
sheep did not produce viable embryos. The attempt to clone a banteng
bull was more successful, as were the attempts to clone mouflon
(a form of wild sheep), both resulting in viable offspring. In 2005 a dog
, was cloned by Korean stem cell
researcher, Hwang Woo-Suk
Cloning may eventually become a viable tool for preserving endangered species and could be important in the future production of transgenic livestock.
However, animal conservation professionals point out that cloning does not alleviate the problems of loss of genetic diversity (see inbreeding) and habitat, and so must be considered an experimental technology for the time being, and all in all would only rarely be worth the cost, which on a per-individual basis far exceeds conventional techniques such as captive breeding or embryo transfer.