Fathers with unhealthy lifestyles can pass on ill effects to their children. However, while there is plenty of evidence to suggest this occurs, our understanding of the mechanisms is lacking. A study on mice has demonstrated a path for altering mouse sperm, leading to noticeable changes in the next generation. The work gives researchers pointers for investigating epigenetic transmission in humans.

Many things can go wrong during a pregnancy that can affect a child's health, but it wasn't all that long ago that it was thought a father's pre-conception environment didn't matter – that his only biological effect on the child was through his genes. We now know environmental factors can modify the extent of a gene's expression, a process known as epigenetics. Exposure to harmful chemicals or an unhealthy diet can alter sperm, with consequences for subsequent generations.

Dr Patrick Western of Australia's Hudson Institute has explored the role of the PRC2 gene in this process, publishing his findings in BMC Biology. Despite aiming to understand the influence of environmental factors, Western used a genetic mutation as a tool.

“Sperm only carries one copy of the genome,” he told IFLScience, but most of the way through development they have both. Right at the end they go through meiosis and only have one copy.”

Some of the mouse sperm Western investigated started with a healthy PRC2 copy, along with a mutation, while others had no healthy copies. Even though the healthy version had been deleted by fertilization, it still left a legacy on the sperm, which was not seen in those that never had a normal PRC2 gene.

Mice born from fathers with no good PRC2 copies had some genes turned on that would normally be turned off, and vice versa. Their development progressed at different rates from their counterparts. They appeared normal when fully grown, but Western told IFLScience this may only have been because his team didn't measure their metabolism or behavior.

PRC2 is a highly conserved part of the genome, present in fruit flies as well as mammals.

“Now we’ve shown that PRC2-dependent epigenetic changes in sperm can be ‘inherited’ by offspring from their fathers, we can start to look at whether specific foods or chemicals might positively or negatively affect PRC2 function and therefore development in children,” Western said in an emailed statement. Ultimately, such understanding may lead to ways to interrupt the transmission of negative traits.

Since PRC2 is not the only way in which ill health can transfer from father to child, even if it is not influenced by particular lifestyle factors, other epigenetically influenced genes may well be. “When thinking of starting or adding to their family, both mum and dad should try to be as healthy as possible,” Western said.