(Rainis Venta. Image rights: Creative Commons Attribution-Share Alike 3.0.)

It's been a billion years since we shared a common ancestor, but yeast -- a simple, single-celled fungus -- is still a distant cousin on our family tree. In fact, even this distant relation has enough in common with us to swap out genes and survive.

In a study published Thursday in Science, researchers report successfully swapping out some 450 of the genes in baker's yeast with similar ones from a human. Each swapped gene got its own strain of yeast, so hundreds were created. With about half of those swaps, the yeast survived as a human-yeast hybrid.

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Even after a long evolutionary separation, humans and common yeast actually have thousands of genes in common -- ones that seem to have the same biological origin and serve the same purpose. To test just how similar those analogous genes have stayed throughout the eons, the scientists swapped out the ones that yeast truly needs in order to survive.

So the fact that these hybrid yeasts survived shows just how closely related all living things are. And yeast probably has hundreds more genes that it could borrow from humans.

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"Cells use a common set of parts and those parts, even after a billion years of independent evolution, are swappable," study author Edward Marcotte of University of Texas Austin said in a statement. "It's a beautiful demonstration of the common heritage of all living things -- to be able to take DNA from a human and replace the matching DNA in a yeast cell and have it successfully support the life of the cell."

Marcotte and his colleagues also found out something about the key to a successful swap: The actual similarity of the genes didn't seem to be a good indicator of whether they'd keep the yeast alive. But if one gene from a particular module -- a group of genes that work together -- was swappable, the rest of its module likely was as well (and vice versa).

The scientists won't be creating gingerbread frankensteins anytime soon, but they hope their yeast strains can be used to study how defective genes that cause human disease react to different therapies.

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