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Biologists report the first monkey "chimeras", born with a mix of genes in their cells.

The monkeys were born from mixtures of very-early stage embryonic cells. That suggests that primate (including human) embryonic stem cells may have developmental differences not present in mouse stem cells, ones seen as their equivalents in research until now. Also, the research points to a new strategy for cloning primates using embryonic cells, say the study authors, an achievement that has eluded researchers for more than a decade.

Reported by the journal Cell, the study team led by stem cell developmental biologist Masahito Tachibana of the Oregon National Primate Research Center, reports three healthy male monkeys were born from their efforts. Rather than using embryonic stem cells cultured from lines of cells grown in petri dishes, the researchers used early-stage stem cells taken directly from monkey four-cell embryos to create 10 chimeric, or genetically mixed, embryos. The teams combined cells taken from different early-stage embryos to make new chimeric ones, and then implanted them into female monkeys.

Three of the embryos were carried...