two scientists in the us have questioned the credibility of Dolly. They say that the experiment must be repeated before its results are accepted. No other scientist has reported cloning a mammal form an adult cell. Citing reasons for their skepticism, Norton Zinder of Rockefeller University, New York, usa and Vittorio Sgaramell of the University of Calabria, Italy, say that the cloning was successful once out of 400 trials. One successful attempt out of some 400 is an anecdote and not a result.
In a letter to the Journal Science , the scientists say that the birth of Dolly was stunning because she was cloned from dna taken from an adult mammalian cell. The cell was taken from a pregnant Ewe. They speculate that the critical dna has come from a stray foetal cell, or a primitive cell from the Ewe, which has not specialised like normal adult cells. According to the scientists, the genetic evidence matching Dolly to the batch of donor cells was "good but not sufficient". Meanwhile, Dolly-cloner Ian Wilmut of the Roslin institute, Scotland, has submitted Dolly's mitochondrial dna for an analysis.