Scientists think they may have solved the question of what makes a person gay.

Scientists from the National Institute for Mathematical and Biological Synthesis suggested Tuesday that the trait it is passed to children by their opposite-sex parent.

A lesbian will almost always get the trait from her father, while a gay man will get the trait from his mother, according to the new study published in 'The Quarterly Review of Biology.'

The authors said they knew homosexuality was not a simple genetic link, because there are many pairs of identical twins who have differing sexual orientation.  This study suggests the trait has an epigenetic, not a genetic link.

The new study claims homosexuality is linked to epi-marks, which are extra layers of information that control how certain genes are expressed.

These epi-marks are usually, but not always, "erased" between generations. But the new study found the epi-marks are not erased in homosexuals. They're passed from father-to-daughter or mother-to-son, explains William Rice, an evolutionary biologist at the University of California Santa Barbara and lead author of the study.