Fertility scientists are joining ethicists and antiabortion activists in criticizing a researcher's claim that he has created chimeric human embryos that are part male and part female. Scientists doubt the usefulness of work presented by Norbert Gleicher last week at the annual meeting of the European Society for Human Reproduction and Embryology (ESHRE) in Madrid. ESHRE condemned the work immediately after it was presented.

Gleicher, who could not be reached for comment, reported that he and his colleagues at the Center for Human Reproduction in Chicago had transplanted one, two, or three cells from male embryos into 21 one-day-old female human embryos. His rationale was that the Y chromosome in some cells made the fate of the cells simple to monitor. Twelve chimeric embryos developed normally, he said, while four died immediately after the cell transplant and five developed into abnormal blastocysts.

The chimeras were destroyed after 6 days, at...

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