A Science Odyssey
People and Discoveries

Search for behavioral genes

Study Links Genes to Homosexuality reported the Washington Post. Is There a Gay Gene? USA Today chimed in.

A self-proclaimed "obscure molecular geneticist," Dean Hamer, had conducted a study in the early 1990s that showed a correlation of a DNA marker on the X chromosome with homosexual men that was higher than random distribution would have been. The study had looked at extended family histories and at the DNA of gay men. Researchers found that a tiny portion of the X chromosome appeared the same in a surpringly high proportion of gay brothers. Hamer's team did not find a so-called gay gene, but found evidence to suggest such a thing existed. The results were printed in the journal Science in June, 1993, sparking headlines that ranged from seriousness to tabloid silliness.

The article appeared just as President Clinton was pushing for a new policy of tolerance of homosexual people in the armed services. What Hamer, and many others, found was the fact that "the genetics of behavior, and sexuality in particular, is an emotionally and politically charged topic."

Equally as controversial are discussions of genes for intelligence. The X chromosome has helped reveal genes linked to intellectual activity, sparked by the discovery of fragile-X syndrome, the most common form of mental retardation. After Down's syndrome it is the most frequently occurring inherited disease among Westerners. The gene sequence causing fragile-X has been identified, though not entirely understood. It is not an intelligence gene, but one that controls fetal development. Down's syndrome, too, is revealing of the role of genes in development of intellect: most Down's syndrome children are born with an extra copy of one chromosome. This difference amounts to less than 2 percent of the chromosome count, but causes gross impairment of intellect as well as physiological problems. About half of the 50-100 thousand genes individuals inherit from their parents are thought to be involved in brain development. But "nature" is only part of the picture, and its countless twists, turns, and variations make human development far from straightforward.

Advances in the understanding of Alzheimer's disease have helped push discoveries in the relationship of genes and behavior. As with heart disease, a person may have a gene that predisposes him or her to develop symptoms. In some cases the symptoms will occur regardless of behavior, but in most cases there are environmental or "lifestyle" influences that spur development of the disease. Eating fatty foods can cause arteriosclerosis, and drinking lots of aluminum-rich water can cause buildup of amyloid in the brain, a physical cause of Alzheimer's dementia.

The genetic link to a homosexuality and the pursuit of knowledge about each and every human gene has raised ethical and practical questions about searching for genes for violence or aggression, shyness, intelligence, and other behaviors.

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