Scientists say they've identified a single gene that could explain most failures to clone mammals.
Cloning involves taking DNA from a cell of an adult animal and putting it into an unfertilized egg. So the DNA must switch gears, telling the egg how to divide and grow into a new individual. The switchover requires shutting some genes off and turning others on.
The problem with the gene, called "Oct4," doesn't explain every failure, but it could account for about 90 percent, said researcher Hans Schoeler of the University of Pennsylvania's veterinary school in Kennet Square, Pa.