Fig. 1

Heterozygous allelic imbalance through cis-acting regulatory variation. a A mutation in a proximal promoter may prevent transcription factor binding altering expression of the allelic transcript. Marker SNPs (shown here as black/white circles) can be used to determine transcript ratios. b A mutation in a distal enhancer site may prevent combinatorial binding and affect transcription levels. c A mutation in trans will affect both alleles equally and no AEI will be seen