PITTSBURGH (KDKA) — Scientists say when it comes to smarts, it’s the mother that makes the difference.

According to the Independent, a new study shows a mother’s genetics determine how clever her kids are, but the father makes no difference.

Why? Women are more likely to transmit intelligence gene to children because they are carried on the X chromosome. Women have two of these while men have just one.

Additionally, researchers now believe genes for advanced cognitive functions inherited from the father may be automatically deactivated.

A category of genes known as “conditioned genes” are believed to only work if they come from the mother in some cases and the father in other cases. Intelligence is believed to be among the conditioned genes that have to come from the mother.

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Studies utilizing mice show that those with an extra dose of maternal genes developed bigger brains with smaller bodies, while those with paternal genes had small brains and bigger bodies.

Cells with paternal genes accumulated in the limbic system, which focuses on functions such as sex, food and aggression. Researchers did not find any paternal genes in the cerebral cortex, which is where reasoning, thought, language and planning take place.

As for human examples, researchers interviewed 12,686 young people between the ages of 14 and 22 every year from 1994. Despite taking into account several factors, from the participants’ education to their race and socio-economic status, the team still found the best predictor of intelligence was the IQ of the mother.

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