Your sexual orientation develops long before you are born. It is not by chance that you are heterosexual, homosexual, bisexual, etc. and scientific evidence to this fact has been around since the 1980s. In 2014 it was confirmed that the association between same-sex orientation in men and a specific chromosomal region existed. It seems that there is the existence of a complex interaction between genes and environment either in the uterus or after birth that affects this chromosomal region. Research has found that two things entered into the equation. Heritable and environmental components. It was found that although it was thought that perhaps there was a “gay” gene, that was not the case. It occurs through another mechanism known as epigenetics. Epigenetics is the influence that environmental factors have on genes, either before or after birth. Epigenetics identify the molecular mechanisms (epi-marks) that mediate the effect of environment on the gene expression. It is known that epi-marks are generally erased one generation to another, however, under certain circumstances they may be passed on to the next generation.
Normally females have two X Chromosomes and one of the is inactive (switched off). It has been studied and proven that in some mothers who have homosexual sons, there is an extreme skewing of the inactivation of these X Chromosomes. This implicates a region in the X Chromosome in determining sexual orientation.
It has been thought that external factors such as chemicals, toxic compounds, pesticides and medicinal drugs can play a part in creating epi-marks on the DNA. These factors can interfere with the hormones of a pregnant woman, affecting the sex hormones in the development of the fetus and may influence the activity of these hormones in establishing the sexual orientation of the fetus.
Scientist are looking into this region on the X-Chromosone and possible the interaction. However, more evidence is leading investigators to a specific region on the X-chromosome and possibly a region on another chromosome.
This does not mean that homosexuality is a disorder—nor are there mutations in the genes in these regions, which still remain to be identified. It does suggest, however, that there is a specific region on a chromosome that determines sexual orientation.