In a step that could pave the way to using animals as organ banks, scientists at the PPL Therapeutics in Edinburgh, Scotland, the same laboratory that helped produce Dolly the cloned sheep in 1996, have developed a method to selectively modify genes in sheep clones. Although transgenic modification of sheep is fairly well developed, before now, there has been no control over where the gene would turn up or how active it might be. This new method allows scientists to insert new genes or introduce changes into a specific part of sheep DNA and then create clones carrying the altered genes. The research was presented in yesterday's issue of Nature.