Researchers from Iceland discovered that 97 per cent of genetic mutations were caused by the age of the father, while the mother's age had no effect at all, the Daily Mail reported.
Genetic screening was carried out on 78 families with children who were either on the autistic spectrum or had been diagnosed with schizophrenia.
This information was compared with data from hundreds more families with no link to either condition.
Everyone had some genetic mutations, but on average children had an additional two for every year of the father's life.
A 20-year-old father transmitted on average 25 mutations to his child, while 40-year-old fathers, the oldest in the study, transmitted around 65.
The mother transmitted around 15, regardless of her age.
"The number of mutations coming from the mother is constant, which makes sense as her eggs are formed before she is born, whereas men constantly generate sperm through to old age," lead author Dr Kari Stefansson, of deCODE, a genetics firm in Reykjavik, said.
"The very important conclusion we can draw from this is that the concern focused on the increasing age of mothers is probably misplaced. They may be off the hook, and men are on it
