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BOB HIRSHON (host):
Twin inheritance. I’m Bob Hirshon and this is Science Update.
Fraternal twins run in families, and now scientists have identified why. Geneticist Hamdi Mbarek at Vrije University in Amsterdam and his colleagues compared the genomes of thousands of women who had given birth to twins to those who had not. The researchers report in the American Journal of Human Genetics that the mothers of twins were more likely to have variants of two key genes.
HAMDI MBAREK (Vrije University):
The first gene, FSHB, increases the chance to have fraternal twins by 18%, and the second gene, SMAD3, increases the chance by 9%.
Women with variants of FSHB produce more of a hormone that promotes egg development. And a variant of SMAD3 makes their ovaries more responsive to the hormone. Both result in the ovulation of multiple eggs at the same time, which can lead to twins. I’m Bob Hirshon, for AAAS, the science society.