Viruses are nasty things. Even the most benign are parasites, draining the resources of their hosts. The less benign can cause lethal diseases. But evolution is ever resourceful, and in one case it has found a way to harness a viral gene for the host's benefit. A paper just published in the Proceedings of the National Academy of Sciences, by Kathrin Dunlap of Texas a&m University and her colleagues, shows that this gene plays a vital role in the development of some embryos. The gene in question belongs to a retrovirus and the embryos in question belong to sheep. But Dr Dunlap's work has implications for other mammals, including people.
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