A new study shows a possible link between a man's age and the chance his child will develop mental illness.
An Icelandic company says 97 percent of DNA mutations come from the father.
Researchers found a 40-year-old man passes on almost three times as many mutations in DNA to his child than a 20-year-old.
Scientists believe men are responsible because women have all their eggs at birth, while men constantly develop sperm.
