Biologists have long attempted to pinpoint why some traits exhibit greater variation than others. While they have known that traits essential for survival are less variable than traits like hair color, which have little to no effect on fitness, new research has demonstrated the importance of another factor: gene location.

In an article published in the Oct. 15 issue of Science, Princeton U. ecology and evolutionary biology professor Leonid Kruglyak and his collaborators — Sonja Skrovanek, a former researcher at Princeton’s Lewis-Sigler Institute for Integrative Genomics, and New York U. professor Matthew Rockman — showed that the location of a gene on its chromosome plays a significant role in determining its influence on how traits vary.

For their research, the scientists analyzed almost 16,000 traits in more than 200 C. elegans worms.

Thousands of genes reside on each chromosome, controlling the expression of different physical traits in individuals. The combination of alleles, or different forms of a gene, strongly influences the expression of a particular trait.

The researchers found that genes contributing to genetic variation were disproportionately located on the ends of C. elegans chromosomes, even after accounting for such factors as the relative importance of traits to survival.

They devised a mathematical model to show how such a distribution might occur. It indicated that genes are affected by natural selection’s effects on neighboring genes. Genes near the centers of chromosomes have more neighbors, making them more susceptible to the effects of natural selection, which tends to eliminate variation.

The researchers said their approach allowed them to observe the effects of natural selection.

“We have used quantitative genetics in C. elegans to show that randomization in this … species is ineffective, diminishing the ability of natural selection to evaluate individual alleles,” the researchers wrote.

Their work suggests that the structure of chromosomes may sometimes force natural selection to evaluate genes together rather than individually.

“The evolutionary fates of alleles — and hence phenotype — are determined less by their own effects than by the genomic company they keep,” the researchers said in the paper’s conclusion.

The study was funded by grants from the National Institutes of Health, among other sources.