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The Gene Nursery

Some genes crop up through accidental duplication of existing genes, but so-called orphan genes seem to arise through different means, writes Carl Zimmer in the New York Times.

"[Orphan genes] looked like perfectly normal genes, except they were only found in one species,” Anne-Ruxandra Carvunis, an evolutionary biologist at the University of California, San Diego, tells Zimmer. "There was no explanation for how a gene could be in one species and not in other ones."

These genes appear to emerge when a stretch of DNA is mutated into a stretch encoding a start codon that the cell may then recognize process to make a protein.

"It takes only a modest mutation to non-coding DNA to get a cell to read some non-coding DNA and treat it like a gene," Zimmer adds at his blog, the Loom.

Then, as Aoife McLysaght, a geneticist at Trinity College Dublin, tells Zimmer in the Times, natural selection can begin to "sculpt" them.

Such de novo genes, as David Begun, an evolutionary geneticist at the University of California, Davis has dubbed them, may often be lost, but some can develop key role or be involved in disease. The NCYM gene, for instance, is a de novo gene only found in humans and chimpanzees that plays a role in childhood brain tumors.

"I sometimes think of the genes in an organism as the musicians in an orchestra. As each gene evolves, I imagine each musician playing a new melody," Zimmer adds at the Loom. "But evolution can invite new musicians to pull up a chair and add their music to the song."