Scientists from the University of California, Los Angeles (UCLA) have announced that they can now predict whether a man is a homosexual based on his DNA, and all that is needed is a swab of his saliva, according to New Scientist.

The researchers, led by openly gay scientist Tuck Ngun, said in the test they conducted they were able to correctly predict if a person is a homosexual or not by examining 400,000 epigenetic tags, or "chemicals that latch onto DNA and help turn genes on or off."

The study, the findings of which will be presented at the American Society of Human Genetics annual meeting in Baltimore this week, involved 47 sets of male twins—37 of which were both gay, while 10 pairs differed.

The researchers particularly looked at the levels of methylation, or biochemical process, across the genome, or full DNA sequence, of each twin, and came up with a spreadsheet collecting this data.

The scientists then studied the genomes of the homosexual and heterosexual volunteers, using an algorithm to look for specific gene regions in which methylation patterns differed significantly between the two groups.

Five gene sites were then identified: three regions of "junk DNA" whose role is still unclear, another region of genes believed to affect sexual attraction, and another gene region thought to be responsible for making a protein that affects neuron function.

Using test results from 20 of the male twins, the team of researchers then set out to build a model if a person is gay or straight, based on the methylation patterns of their genes.

This model, as it turned out, was able to predict homosexuality 67 percent of the time.

Ngun said that if epigenetic tags indeed have an effect on sexual orientation, the next challenge will be to determine at what age the marks appeared and whether they were permanent.

"Assuming the marks were placed early enough in foetal development, the potential for a [screening] test is there," the lead researcher explained.

He added that he hopes his work will be used for purely scientific purposes, and not to punish homosexuals.