Researchers have finally brought the controversy around 'gay gene' theory to an end. A study conducted on gay siblings revealed the existence of genetic material on an X-chromosome segment which may be responsible for homosexual preference in males, though not so in females. Dean Hamer and his colleagues at the National Cancer Institute, Washington, took blood samples of homosexual and heterosexual siblings for DNA comparison. The fact that gay men had more gay relatives on the maternal side heightened the possiblity ofX-chromosomes carrying the gay gene.