In a fascinating new study, genetic links in humans have found that birds of a feather actually do flock together. The DRD2 (dopamine receptor) marker that is associated with alcoholism appears to form friendships with others who have the same gene. Those that do not possess the gene formed relationships of their own together. However genetically speaking, opposites also attract, and this is caused by another type of DNA characteristic. People who had a gene associated with an open personality, CYAP26, tended to have friends who did not share this gene.

James H. Fowler, of the division of medical genetics at the University of California, San Diego explains:

"We live in a sea of genes. What happens to us may not depend only on our genes but on the genes of our friends. This might be the first step towards understanding the biology of 'chemistry,' the feeling you have of you whether you like or dislike a person [almost immediately]. We might choose friends not [only] because of social features we consciously notice but because of biological and even genetic features that we unconsciously notice. "

A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify cells, individuals or species. It can be described as a variation that can be observed. A genetic marker may be a short DNA sequence, such as a sequence surrounding a single base-pair change, or a long one, like minisatellites.

Published in the Proceedings of the National Academy of Sciences, Fowler and researchers used data from the National Longitudinal Study of Adolescent Health and the Framingham Heart Study. The study was controlled for factors like simply living in the same region, that could also account for the connections between friends.

DRD2 is involved in producing a type of dopamine receptor, and the researchers report that people with a variant linked with increased risk for alcoholism were more likely to be friends with each other. Those with the variant were 10% more likely to be associates than would be expected by chance. Since most of the participants in the adolescent database were just 14 at the time they were studied, it is not probable that these subjects met in drinking environments, which might otherwise explain the connection.

Fowler continues:

"It's true that if I'm more impulsive, I might choose to be with friends with others who are more impulsive. There can be a feedback effect. We know that [this gene] shows an association with alcoholism. Now the evidence here is that if you have this gene, your friends are more likely to have it. You're not only susceptible biologically to this behavior; you're also more like to be surrounded by people who are susceptible to this behavior."

On the other hand, a gene that codes for a protein that affects how the liver metabolizes foods and drugs but is also linked with openness to new experience, is associated with the opposite tendency. Those who share a version of this gene prefer people who aren't like them or have the same tendencies and habits.

Fowler concludes:

"It's important to fully understand not just what's biologically going on with you as an individual but biologically what's going on as a group. It's not just both nature and nurture: our nurture is in part nature."

Genetic markers can also be used to study the relationship between an inherited disease and its genetic cause. It is known that pieces of DNA that lie near each other on a chromosome tend to be inherited together. This property enables the use of a marker, which can then be used to determine the precise inheritance pattern of the gene that has not yet been exactly localized.

Full Study Detail: PNAS

Written By Sy Kraft, B.A.