By Matt McGrath
BBC News
**Researchers in the US have genetically engineered fruit flies so that their sperm glows in the dark.**The scientists from Syracuse University say that by making the fly’s sperm glow green or red they can learn more about the battle to fertilise eggs.
Scientists regard this type of sexual selection as a very important force for evolutionary change.
The glow allows researchers to observe in striking detail what happens to live sperm in the female after copulation.
‘Knocked us out’
In nature, monogamy is often the exception, promiscuity usually the rule.
But whenever a female of any species mates with more than one male there is a bizarre battle between the sperm of the potential fathers as they attempt to fertilise the eggs.
The Syracuse University researchers, writing in the journal Science, say the glow has allowed them to shed light on this mysterious process.
Prof Scott Pitnick, one of the authors of the research, says it was a jaw-dropping moment when he saw the multicoloured sperm through the microscope for the first time.
“It far exceeds our expectations in that we can essentially track the fate of every sperm the female receives,” Prof Pitnick said.
“It’s seeing all the novel observations, the complexity of what sperm do inside the female reproductive tract that no-one has ever been able to observe before. That’s really knocked us out.”
Prof Pitnick and his colleagues are now busy creating glowing sperm for other species and he says the technique could be widely used to understand not just issues of evolution but to potentially solve problems of fertility in humans.