Whose genes determine a child’s intelligence?

Dear Doctor,

Is it true that a child’s intelligence is inherited from its mother? What aspects other than the sex of a child does a man contribute genetically? Michelle

Dear Michelle,

Traits are passed from parents to their children through DNA. A child may inherit some genes from the father and some from mother, depending on the ones strongly present in either. Genes for some diseases are carried by the mother, but a male child develops the disease (sex linked recessive disorders like hemophilia, colour blindness).

However some studies suggest that intelligence is inherited from the mother. These findings were initially found in studies on mice, but confirmed when extrapolated to human brains. This was carried out by a study conducting a survey on >12,000 people. Paternal genes tend to accumulate in the limbic system, which is concerned with aggression, hunger, e.t.c. basic instincts. No paternal gene is found in the cerebral cortex, which is concerned with advanced functions like learning, reading, e.t.c.

Intelligence genes are carried by the X chromosome, which are 2 with women. Even if it comes from the X chromosome of the father, it gets deactivated. Mitochondria are inherited exclusively from the Mother. Metabolic energy is supplied in the body by mitochondria, which is consumed voraciously by the brain. Thus better mitochondria can be presumed to translate into better brain function.

However only about 40-60% intelligence is inherited. More than passing on intelligence genes, a mother contributes to the child’s intelligence by close bonding, building up the confidence of the child and providing a suitable environment, where the child can enhance his skills and use his intelligence.