eQTL for Dummies – Intro
What the hell are eQTL (expression Quantitative Trait Loci)?
Let’s start by the beginning, What is a “quantitative trait”? It’s any phenotype that can be quantified, in other words, anything we can measure about the phenotype of a given organism, e.g. we can measure height, fat, skin color, etc, etc. any of those can be a quantitative trait.
Ok, easy enough, but what is a “quantitative trait loci” (QTL)? It’s a quantitative trait -a measure of the phenotype- that is associated with a particular loci, in normal human language: QTL are phenotypes associated with a sequence in the DNA. That DNA sequence have a direct effect on the measure of phenotype, taking the ‘fat’ example, suppose that if you have a determined sequence in your DNA sequence, you will have more or less fat that if you don’t have that sequence.
What about the expression? We are talking about the expression of genes, how much of each gene is being produced by the target cells. So, a quantitative trait is anything we can measure, can we measure gene expression? Off course we can! That’s what microarrays are made for, that is their whole reason of existence.
To conclude, we are measuring the quantity of genes produced by each cell and looking if those changes in expression of the genes can be because of a given DNA sequence.
What are eQTL useful for?