Do twins always skip a generation?
THE CLAIM: Twins always skip a generation. THE FACTS: People with twins in their extended families may wonder whether a crib for two is in their future, too. According to conventional wisdom, twins not only run in families, but they also — for some strange reason — always skip at least one generation. It is a claim that is widely repeated, but only partly true. Scientists have known for some time that there is a gene that can predispose women to hyperovulation, or releasing two or more eggs in a single menstrual cycle. When both eggs are fertilized, the resulting siblings are fraternal twins. Because this gene can be passed on, the tendency to have fraternal twins can, in fact, run in families. Identical twins, on the other hand, result from one fertilized egg randomly splitting in two, creating two siblings with identical DNA. Because there is no known gene that influences this process, it is considered a mere coincidence when one extended family has multiple sets of identical twins
