Genetics and gene regulation · BEGINNER LESSON
Expression quantitative trait locus
An expression quantitative trait locus, or eQTL, is a genetic variant linked to differences between individuals in the expression level of a gene. In practice, it is used to test whether a DNA change is associated with higher or lower gene activity in a measured tissue or cell state.
What it is and what is measured
An expression quantitative trait locus (eQTL) is a DNA variant that is statistically associated with inter-individual differences in gene expression level. The measurement is usually a gene’s expression in a tissue, cell type, or condition, and the goal is to find variants that help explain why people differ in that measurement. Standard studies often examine healthy adult tissues under baseline conditions, while other studies test specific cell types or conditions. [0,1]
[1] Integrating axis quantitative trait loci looks beyond cell types and offers insights into brain-related traits [2] Beyond the baseline: mapping the context-specific regulatory ...
How eQTLs work
The basic idea is that a regulatory variant changes how strongly a gene is expressed. The sources describe several ways this can happen: the variant can alter a transcription factor binding site, change enhancer activity, or act only when chromatin accessibility, transcription factor abundance, or splicing efficiency shifts in a particular context. Because the effect may depend on a tissue, environmental exposure, treatment, or developmental state, some eQTLs are context-specific rather than always visible. [1]
[2] Beyond the baseline: mapping the context-specific regulatory ...
Why they matter
eQTLs help connect noncoding variants to gene regulation, which is useful because many disease-associated loci are outside protein-coding regions and are suspected to act through regulation. Studies can also compare eQTLs with disease-associated variants to ask whether the same locus affects both expression and disease risk. [1]
[2] Beyond the baseline: mapping the context-specific regulatory ...
Limitations and measurement gaps
Standard baseline eQTL studies can miss effects that appear only in rare cell types, after perturbation, or in other nonbaseline states. The sources also note that single-cell eQTL studies can be underpowered for uncommon cell types because fewer reads are available and measurements are noisier. More generally, eQTLs estimate only the genetic component of expression variability and may not capture all regulatory effects or all variant types. [0,1,2]
[1] Integrating axis quantitative trait loci looks beyond cell types and offers insights into brain-related traits [2] Beyond the baseline: mapping the context-specific regulatory ... [3] Deep-learning prediction of gene expression from personal ...
SEE THE IDEA
How an eQTL is identified
A difference in the genome that may affect regulation.
How much RNA from a gene is observed in a tissue or cell state.
Testing whether one tracks with the other across individuals.
A variant linked to expression differences.
DNA variant and expression are measured across individuals; an association between them supports an eQTL.
eQTLs are found by matching genetic differences with measured expression differences, then asking whether the link is stronger than expected by chance. [0,1]
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.