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The Strange Case of a Man Who Is Both His Son's Father and Uncle

Human chimera gives birth to genetically distinct child.

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When a Washington man failed a paternity test, he was understandably concerned. That concern undoubtedly increased when he was told that it was his twin who was the father of his child—especially since the man had no twin. At least not one that was ever born.

The man is a chimera, a person who has two distinct sets of DNA. In this case, the man had absorbed the genes of his twin in the womb. It is theorized that “vanishing twin syndrome,” where one twin dies and is absorbed by the other, occurs in between 20 and 30 percent of pregnancies with multiple babies. About one in eight single childbirths are thought to start as multiple pregnancies.

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