From Nature:
The textbook rule that says activated human genes almost always express both of their copies — the one inherited from mum and that inherited from dad — seems not to be true. Instead, a good chunk of our genome could prefer the ‘single life’, according to new research.
Whether the maternal or paternal copy gets switched on in such cases seems to be random. But the result could have a big impact on disease susceptibility and other biological traits. It had been thought that there are only a handful of situations in which just one of a pair of gene copies is used. But a new screen of 4,000 human genes has uncovered 371 that sometimes play favourites, suggesting that this phenomenon is far more pervasive than had been thought. This kind of selective gene expression could create an extra source of variation between people, even when some of their genes are identical. “I like the idea that we’re all mosaics, and this might contribute to differences,” says Steve Henikoff, a biologist at the Fred Hutchinson Cancer Research Center in Seattle, Washington.
More here.