Dog breeds have been selected over the years for particular characteristics with regard to physical appearance, behaviour and usefulness to their owners – guarding, shepherding, hunting, cuddling. They are already quite inbred, and therefore genetically similar, although not to the extent of clones. A clone and its original (in this case the dog Booger) are almost like identical twins. They share the same DNA and genes that make up the genome – the blueprint for life.

But, as with identical twins, this does not mean that clones will be indistinguishable. Identical twins and cloned animals often differ quite substantially in their behaviour and they can have physical differences, although these tend to be subtle. The same blueprint can be read in different ways: genes have to be activated at the right time and place, and this is controlled in part by processes often referred to as “epigenetics”.

This control can be subject to pure random variation or it can be influenced by external factors, such as nutrition. A group of cloned cattle, despite all having the same original donor, can have quite distinct patterns of coat colour.

Behaviour is also clearly determined in part by genes (as evidenced by the different genetic make-up of separate dog breeds). These genes can be affected by these epigenetic processes, which will give some variation. But even more so than physical appearance, behaviour is also a product of environment and upbringing, as evidenced by identical twins brought up apart.

Clones are even more likely to vary from one another and from the original animal than identical twins do from each other. The wombs in which they developed were different. The clones are likely to be fed differently and kept in an environment distinct from that of the donor dog. The owner can try to treat the clones as she did Booger, but she herself is different (older, wiser?) and has different expectations – the puppies are under pressure to behave like Booger, whereas Booger was not. Finally, cloned animals can develop problems, some of which can be terminal. For example, severe obesity is common in cloned mice. These problems are caused by faulty reprogramming, where one or a few or perhaps even many genes do not act as they should. I am willing to bet that the Booger clones will not end up quite like the original. They will be similar, perhaps a little more so than unrelated pitbull terriers, at least to look at. They may develop some problems or age faster. But, given how aggressive some members of the breed can be, I would not trust the clones all to be protective, as Booger seems to have been. Robin Lovell-Badge is head of stem-cell biology and developmental genetics at the National Institute for Medical Research

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