Dolly - First mammal to be
cloned
Dolly was a female domestic
sheep, and the first mammal 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, part of the University of Edinburgh. She
was born on 5 July 1996 and she lived until the age of six, at which point she
died from a progressive lung disease. 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 part of the body could
recreate a whole individual.
Dolly was created using the
technique of somatic cell nuclear transfer, where the cell nucleus from an
adult cell is transferred into an unfertilised 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. Dolly was the first clone produced from a cell taken from
an adult mammal. The production of Dolly showed that genes in the nucleus of
such a mature differentiated somatic cell are still capable of reverting to an
embryonic totipotent state, creating a cell that can then go on to develop into
any part of an animal. Dolly's existence was announced to the public on 22
February 1997.
Dolly lived her entire life
at the Roslin Institute in Edinburgh. There she was bred with a Welsh Mountain
ram and produced six lambs in total. Her first lamb, named 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 four, Dolly developed arthritis and began to walk
stiffly, but this was successfully treated with anti-inflammatory drugs.
On 14 February 2003, Dolly
was euthanized because she had a progressive lung disease and severe arthritis.
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, which is a fairly common disease
of sheep and is caused by the retrovirus JSRV. Such lung diseases are a
particular danger for sheep kept indoors, and Dolly had to sleep inside for
security reasons.
After cloning was
successfully demonstrated through the production of Dolly, many other large
mammals have been cloned, including horses and bulls. Cloning may have uses in
preserving endangered species and may become a viable tool for reviving extinct
species. Cloning of domesticated animals could be important in the future
production of transgenic livestock.
