A genome is a genome is a genome? Not always. Turns out that many people can have more than one genome in their body at once. Now that sequencing has become cheaper to do, all sorts of interesting data like this is popping up. From the NYT:
Scientists are discovering that — to a surprising degree — we contain genetic multitudes. Not long ago, researchers had thought it was rare for the cells in a single healthy person to differ genetically in a significant way. But scientists are finding that it’s quite common for an individual to have multiple genomes. Some people, for example, have groups of cells with mutations that are not found in the rest of the body. Some have genomes that came from other people.