A new study in fruit flies has found that genetic mutations in mitochondria, inherited from the mother, are an important cause of male infertility.
"What we've uncovered here is an evolutionary process that can explain why male infertility is so common," said evolutionary biologist Dr Damian Dowling of Monash University in Melbourne.
"Our study is essentially the first evidence for the 'mothers curse,'" added Dowling.
They gathered mitochondrial DNA from a diverse range of fruit flies around the world and inserted it into flies that had identical nuclear DNA.
They found that the different mitochondrial DNA affected the expression of about a 1000 nuclear genes in males, but had no effect on the same genes in females.
"The maternal transmission of the mitochondrial genome results in a process which we call the sex-specific selective sieve - mutations are getting through the sieve of natural selection," said Dowling.
"The top 300 of these differentially expressed genes are located within the male testes or in the glands that are responsible for producing the ejaculate," said Dowling.
"It basically points firmly at the idea that males harbour this load of mutations within the mitochondria that are all teaming up to effect male fertility in a detrimental way," added Dowling.
The study has been published in the journal Science.