CLONES are identical, aren鈥檛 they? In popular culture at least, this is the chief reason for using the technique. The first inkling that science fiction writers and Hollywood had it wrong came last year with the birth of CC, a cloned tortoiseshell cat with different markings from its progenitor. Now, research on cloned pigs reveals that more 鈥� much more 鈥� can vary. If you thought having the same genes makes clones behave or even look the same, think again.
The work comes from Jorge Piedrahita of North Carolina State University and colleagues from Texas A&M University. They found that, as expected, some attributes 鈥� such as the levels of albumin and calcium in blood 鈥� varied less in clones than in a control group of naturally bred pigs. Yet a surprising variety of other traits 鈥� including blood glucose and globulins, hair type, number of teats and weight 鈥� fluctuate as much in clones as in controls (Applied Animal Behaviour Science, 21 May, p 321).
This latter group of characteristics, like the pattern of CC鈥檚 coat, are influenced by environmental factors and 鈥渆pigenetic鈥� controls that affect gene expression. Epigenetic controls are delicate and easily damaged during the cloning process. In some cases, such changes cause gross deformities or abortion, but in others they create the subtle alterations that Piedrahita鈥檚 team spotted.
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The consequences are far reaching. One proposed use of cloning, for example, is to provide uniform subjects for animal tests. For this to work, researchers will have to be sure that the traits they want to keep constant do not fluctuate in their clones. The work also highlights the need for researchers who generate stem cells by cloning to screen the cells for abnormal gene expression.
In an upcoming issue of Biology of Reproduction, Piedrahita鈥檚 team goes further, showing that the behaviour of clones in a litter can vary just as much as pigs in a naturally bred litter. Once again, this reinforces the notion that environment has a strong influence on some characteristics. Bob Lanza of Massachusetts-based Advanced Cell Technology, for example, has pointed out that herds of cloned cattle develop hierarchies with dominant animals and submissive creatures. Other traits, though, seem to be more strongly linked with genes: Lanza also talks of clones being just as nasty as their progenitor.
We should not be too surprised by such results, since identical twins have distinct personalities. And so long as cloning alters epigenetic controls, clones are likely to harbour more differences than identical twins. For people who think cloning can bring back a dead pet, the news is bad: a clone may not look or behave like the original. More widely, the findings reveal the uncertainty still at the heart of cloning. So long as this remains, it brings home more strongly than ever that reproductive cloning of humans is irresponsible.