Why is it that when different persons are exposed to similar external factors such as dehydration, heat or sudden bad news, some faint while others don't? Clearly many factors are at play, but one that has just being identified is "genes". Put in another way, there is now evidence that some people are more genetically programmed to have fainting spells than others. The "fainting gene" was found in part of chromosome 2, which is one of the 46 chromosomes that each of us carries. Notably, the effect of the fainting gene was stronger in women because women who had the gene had about three times the risk of fainting compared to men who had the gene.