Some animals may be 'unclonable'

US researchers working on mice have reported that some animals may be 'unclonable' because of their genetic make-up.

Their findings, reported in this month's Nature Genetics, show that some strains of mice may have more clone-friendly genes than others. 'We didn't expect it, but we found tremendous variability', said William Rideout of the Whitehead Institute for Biomedical Research. The researchers cloned seven live animals from 227 embryos using one strain, but they were unable to get any live births from 418 embryos of another strain.

Sheep, mice, cows and goats have all been successfully cloned using nuclear transfer techniques, in which the nucleus of a donor cell is implanted into an egg stripped of its own genetic material. One explanation for the 'unclonable' mice may be that the genes that reprogramme the donor egg may not be active enough.

These recent findings suggest that plans to clone endangered species may fall flat. 'The possibility of a genetic block against this technique could have some serious repercussions', said Rideout.

Ian Wilmut, head of the team that created Dolly at the Roslin Institute in Edinburgh, agrees that the findings are important but adds: 'As time goes on nuclear transfer techniques have improved rapidly, and I'd guess that there may one day be ways of cloning anything.'