Darwin’s theory of Evolution got a jolt on 5th July 1996 when the first cloned sheep Dolly took birth at the Roslin Institute in Scotland. Dolly was named after Dolly Parton, the singer, and the technique that became famous with her birth is called the Somatic Cell Nuclear Transfer. The birth of the first cloned sheep was announced to the world on 22nd February 1997 and it triggered off a series of debates on the ethics of cloning.
The technique behind Dolly’s birth
Headed by Ian Wilmut, Dolly’s birth was engineered by a research team, whose main goal was the faithful reproduction of animals who are genetically modified to produce the therapeutic protein-enriched milk. Dolly was the first mammal to be created from fully differentiated adult mammary cells, by using the Somatic Cell Nuclear Transfer technique. By this technique, a cell is placed in a denucleated ovum, fused by an electrified charge and then an embryo is developed. It is then inserted into the uterus of another sheep as in case of artificial insemination.
The Finn Dorset Lamb Dolly, the first cloned sheep, died on 14th February 2003, at an age of 6 only. She had died from a progressive lung disease and the signs of her illness became evident from January 2002, when she developed a debilitating arthritis at an early age of 5 years.
Usually, her breed of sheep normally lives for ten to twelve years. According to certain researches, Dolly may have been susceptible to premature aging owing to the shortened telomeres that she inherited from her donor sibling (of 6 years age) during cloning. This is called premature senescene. However, there is no conclusive proof of this and as per the necropsy done after her death, she had died from Ovine pulmonary adenocarcinoma, a common disease of the sheep kept indoors.
The legacy of cloned sheep
Post Dolly, several mammals like horse, cow, pigs, mice, rats and bulls have been cloned. Monkeys have been cloned too, using an identical process to embryo splitting. Human cloning was also started in 1993 but hasn’t made much progress due to fierce controversy. Currently, cloning is being used to preserve endangered species. However, cloning has often been not-so-successful owing to the limited number of clones and their lower survival rate (3%). To bring a change in this scenario, the Roslin team is experimenting by growing thousands of copies in culture and then infusing them to unfertilized eggs. If this approach becomes successful then it would be possible to make much more precise genetic changes in future.