Have you ever encountered clones? In case you wish to jump the gun and answer in the negative, it might be prudent to think a wee bit longer. This is because the concept of cloning is intertwined with something that occurs naturally. With that clue, you might have deduced that the closest we have to human clones today – or always have had for that matter – are identical twins. Agreed, their genetic makeup isn’t 100% the same, but monozygotic twins are nature’s genetic clones – these individuals are almost genetically identical to each other. These twins, as the name suggests, come from a single zygote, or fertilised egg. When this egg splits in half and develops as two zygotes instead of one in utero, we have two persons in the place of one. Twins are, however, kind of clones of one another, and not that of another individual – the meaning more often associated with the word. It is in this context that Dolly the sheep has become the poster child of cloning. While she might be the sheep that you instantly identify with cloning, she wasn’t the first animal to be cloned. In fact, she wasn’t even the first mammal to be cloned. In the early 1960s, British developmental biologist John Gurdon made cloning possible and succeeded in producing tadpoles from the adult cells of a frog. Among mammals, the first ever cloned animal was another sheep that was cloned from an embryo cell. This sheep was born in Cambridge, U.K. in 1984.Why is Dolly special?Dolly, in fact, wasn’t even the first sheep that scientists at the Roslin Institute at Midlothian, Scotland cloned. Two other sheep, Megan and Morag, were cloned from embryonic donor cells in 1995, the same year that the institute had success with Dolly. Why then – you might be wondering – is Dolly treated with such reverence? That’s because she was the first mammal to have been cloned from an adult cell, something that was thought to be impossible at that time. As recently as the early 1990s, the dominant school of thought was that it was impossible to clone from adult cells that had already differentiated into specific cells. The likes of Megan and Morag were cloned from DNA that was extracted from cells in early stages of development, even before they differentiated. Researchers at Roslin Institute were working on producing genetically modified farm animals that could then pass on a desired trait to the generations that followed. Cloning was their next step in this research.In order to clone Dolly, English embryologist Ian Wilmut and his colleagues took a cell from the udder – mammary gland – of an adult Finn Dorset sheep and extracted its nucleus. Following the extraction, it was implanted into an empty egg cell from a Scottish Blackface sheep. Normal development in a test tube was confirmed after six days, after which the embryo was transferred into a surrogate mother, another Scottish Blackface. Best kept secretAs Finn Dorsets have a white coat and the Scottish Blackface have a black coat, telling if the lambs were those of the surrogate mother or a clone of the donor was going to be easy. There was, however, the gestation period to contend with. A number of normal eggs were produced and implanted into surrogate ewes by scientists. They needed 276 attempts to create a successful clone from an adult cell, but when one of the surrogates gave birth to a lamb 148 days later on July 5, 1996, the white coat and the white face was a clear indicator that they had achieved something historic. Originally codenamed 6LL3, the lamb was given the name Dolly after American singer and actress Dolly Parton. Despite the sensational nature of what they had achieved, those involved had to stay mum for a little longer… for their own sake. Even in the 1990s, research funding for institutes like Roslin depended upon publication in prestigious scientific journals like Nature. These top-tier journals demanded that word should not go out before the publication date. In Dolly’s case, everyone involved was certain that it would be big news once the word got out. They maintained absolute silence as they diligently worked on the paper that was published in the February 1997 issue of Nature. In the abstract of their article “Viable offspring derived from fetal and adult mammalian cells” in Nature, Wilmut wrote that “The fact that a lamb was derived from an adult cell confirms that differentiation of that cell did not involve the irreversible modification of genetic material required for development to term.”