Researchers found that genes chemically silenced by stress during life remain silenced in eggs and sperm, and can actually be passed down to the next generation.
Obtained from detailed DNA scans in developing mouse eggs and sperm, the finding backs up mounting indirect proof from statistical studies that the genetic impacts of environmental factors like smoking, diet, stressed childhoods, famine and psychiatric disease can be passed down to future generations through a process called epigenetic inheritance.
Many geneticists had considered this impossible.
Genes can be switched off by changing DNA through a chemical process called methylation, in which enzymes respond to environmental factors by marking genes with methyl groups that prevent them from working.
However, the idea that genes carrying these epigenetic markings could be inherited is controversial.
A team of researchers led by Jamie Hackett from the University of Cambridge has challenged the findings of the previous studies.
According to previous studies, as sperm and eggs develop any markings added to genes during life are erased to provide a genetic blank slate from which the next generation develops.
Any remaining marks were also thought to be wiped out when an egg is fertilised.
For the current study, the extracted the DNA from mouse primordial germ cells - the precursors to sperm and eggs - at various stages of their development and used markers to spot any methylated genes.
They found that a tiny number of methylated gene regions survived unerased: an average of just 233 out of approximately 25,000 in the germ cells examined.
Still, the work clearly shows that traits resulting from the surviving markings can potentially be passed on.
"What we've found is a potential way things can get through, whereas before, everything was considered to be erased," News Scientist quoted Hackett as saying.