It's neither, according to a paper just published in the April '95 issue of Archives of Sexual Behavior . The genetic study, conducted over a period of six years, began when it was discovered that there was an unusually low ratio of uncles in the families of the mothers of gay children. According to Dr. Turner, there is a gene or genes on the X and Y chromosomes that give rise to our usual heterosexuality. The gene or genes in question may be inactivated by a specific sequence of DNA called trinucleotide repeats. An example of this is the DNA sequence consisting of one cytosine and two guanines.
Sequences containing the nucleotide cytosine are unique.
It is a natural occurrence much like being born with brown or blonde hair.