"Unexpectedly simple" -- a simple genetic basis for a complex trait

Interesting new story in Science this week, about a seemingly complex trait migration in salmon that seems to be explained to an extraordinary extent by a single small genetic element. The trait is more than just a trait: it’s an ecotype, which is a subspecies (sometimes called a “race”) known to be genetically distinct. In the new paper, the species is Chinook salmon.

The observation of a complex behavioral trait being traced to a single gene or a very small genetic element is not unprecedented. I think one of the most dramatic examples is burrowing in wild mice, described by Hopi Hoekstra’s group a few years ago. But it is still a striking thing to see, because we know that lots of traits that are “complex” (and plenty that don’t seem “complex”) are explained by multiple genes interacting.

Here is the first paragraph of the Perspective piece that accompanies the article in Science:

A common assumption in genetics is that complex traits are influenced by many genes, each with small effect. However, a growing number of examples reveal that single genes or gene regions can have a strong influence on phenotypic traits ( 1 3 ). The genetic architecture of a trait has implications for how traits are inherited and how trait variation is viewed in the context of conservation (maintenance and recovery). On page 609 of this issue, Thompson et al. ( 4 ) examine the genetic basis of migration timing in Chinook salmon and find that timing is controlled by a single genomic region containing two genes, GREB1L (GREB1-like retinoic acid receptor coactivator) and ROCK1 (Rho-associated coiled-coil containing protein kinase 1). Genetic variants in this region include single-nucleotide polymorphisms (SNPs) and short duplications that together form distinct haplogroups with linked alleles (inherited together from one parent) that effectively function as small supergenes.

First link is to the Perspective piece and the second is to the article. PDFs sent on request.