According to recent studies, the X chromosomes passed down from mothers to their children are the ones responsible for intelligence genes. Even when fathers pass down an X chromosome, the father's genes responsible for cognitive function may be automatically deactivated. 

One study, conducted with mice, showed that when mice were given extra maternal genes, they had bigger heads and brains but smaller bodies, while when mice were given extra paternal genes had larger bodies but smaller heads and brains. 

Another study dealing with actual humans had similar findings. Researchers in Glasgow found that the IQ of a teen's mother was the best predictive factor for whether the child would also have a higher IQ. Nonetheless, only about 40-60% of a person's intelligence comes from their DNA. The rest of it comes from environmental factors. Although, even in that, mothers play a significant role. University of Washington researchers found that children who were emotionally close with their mothers showed a 10% larger hippocampus on average than children who did not. 

Any other thoughts? Talk to us about them in the comments below, and share with the moms in your life to see what they think!