How is it that a disc-like cluster of cells transforms within the first month of pregnancy into an elongated embryo? This mechanism is a mystery that man has tried to unravel for millennia. The first significant step towards understanding the issue was made nearly a century ago in experiments conducted by the German embryologists Hans Spemann and Hilde Mangold. The two used early newt embryos and identified a group of cells within them which, upon transplantation, formed a two-headed tadpole...
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