This Week in History: 22nd February 1997 Successful cloning of Dolly the Sheep was announced

The successful cloning of Dolly the Sheep was announced to the public on the 22nd of February 1997, after her birth on the 4th of July 1996. Dolly, named after Dolly Parton, was the first mammal to be cloned from an adult cell; this success would have many implications for future research. The cloning was performed in Scotland, at the Roslin Institute in Midlothian, so is on display at the National Museum of Scotland.

Dolly was cloned through the process of somatic cell nuclear transfer. In this process DNA was extracted from a body cell of one sheep (sheep A) and fused with an egg cell without the nucleus removed from sheep B. This fused egg cell developed into an embryo which was placed into the uterus of sheep C, a surrogate mother. When she was born, Dolly’s DNA was identical to that of sheep A. She wasn’t the first animal to be cloned but was the first to be cloned from an adult cell, which was very significant in terms of further research. Dolly was later bred with a Welsh Mountain ram and had a total of six lambs.

Dolly died on the 14th of February 2003, at the age of 6. Dolly was diagnosed with a progressive lung disease and severe arthritis and was found to have ovine pulmonary adenocarcinoma (a form of lung cancer) when examined after death. This is a caused by Jaagsiekte sheep retrovirus, a common disease among sheep, and many others in Dolly’s flock also caught this virus.

Dolly’s cloning was not thought to be connected with her death, despite the life expectancy of the breed to be 11-12. Some scientists speculated that her early death could be a result of her being born with the genetic age of the 6-year-old sheep she was cloned from, but this wasn’t proved.

The cloning of Dolly had a long-lasting legacy in scientific research. Many other large mammals were cloned using the same technique, including horses, bulls and pigs. There was also the potential for the technique to have the ability to preserve endangered species through cloning, or even to revive extinct species with the use of frozen tissue.

A further legacy of Dolly’s successful cloning was in stem cell research: the cloning method showed that it is possible to make a fully developed adult cell act like a cell from a newly fertilised embryo. This discovery could have many implications for regenerative medicine, and research into this has grown significantly since Dolly was cloned.

Image: dun_deagh via Flickr

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