  An expression quantitative trait locus (eQTL) is a chromosomal region where
genetic variants are associated with the expression levels of certain genes
that can be both nearby or distant. The identifications of eQTLs for different
tissues, cell types, and contexts have led to better understanding of the
dynamic regulations of gene expressions and implications of functional genes
and variants for complex traits and diseases. Although most eQTL studies to
date have been performed on data collected from bulk tissues, recent studies
have demonstrated the importance of cell-type-specific and context-dependent
gene regulations in biological processes and disease mechanisms. In this
review, we discuss statistical methods that have been developed to enable the
detections of cell-type-specific and context-dependent eQTLs from bulk tissues,
purified cell types, and single cells. We also discuss the limitations of the
current methods and future research opportunities.
