Simplified overview of hematopoiesis. Hematopoietic stem cells (HSCs) have self-renewal activity (represented as the arrow) and can therefore maintain their numbers. During hematopoietic differentiation, HSCs lose their self-renewal capacity and become increasingly lineage-committed (represented as the gradual loss of colors)

Cis- and trans-regulated gene expression. Cis-regulation is expected to originate from polymorphisms (red triangles) in the regulatory elements (white circles) or the coding region (colored rectangle) of the gene itself (or possibly of a nearby gene) (a). Trans-regulation is expected to originate from polymorphisms in the regulatory elements or the coding region of a gene located distant from the gene whose expression it controls. Note that variation in expression of multiple genes can map to the same gene in trans (b). Transcripts and their eQTLs are graphically depicted in a genome-wide eQTL regulator map. Plotted on the y-axis are the physical positions of all measured transcripts, whereas on the x-axis the genomic regions that are most strongly associated with variation in expression levels (i.e. eQTLs) of the corresponding transcripts are shown. When transcript and eQTL position coincide, the transcript is considered to be cis-regulated and plotted on the diagonal. The vertical transband refers to transcripts encoded by genes that are positioned throughout the whole genome, but map to the same eQTL position. Transband transcripts are suggested to be coregulated. Potential transband regulators are located within the eQTL interval (where the transband meets the x-axis). Figure adapted from Bystrykh et al. 2005 (c). Coregulated transband genes can be directly or indirectly targeted by the potential regulator, thereby creating a network that consists of multiple levels of gene regulation (d)

Overview of (expression) quantitive trait locus mapping procedure. Variation in phenotype (here shown for six individuals) is correlated with variation in genotype (genotypes at a single chromosome are shown for each individual). The genomic location where these two parameters associate most strongly is referred to as the (expression) quantitative trait locus or (e)QTL. In this case, the three genetically distinct individuals that have a high value for the phenotype of interest carry the light blue genotype at the (e)QTL position, whereas the three that have a low phenotypic measure carry the dark blue genotype at that position. The phenotype can either be a classical trait (classical linkage) or the expression level of a gene (genetical genomics)

An overview of the described approaches (left), the sources of analysis (middle) and the phenotypic measures (right)