The technique of pulsed-field gradient electrophoresis (PFGE) allows the determination of gene linkage relationships since DNA fragments up to 2 Mb can be separated. PFGE was employed to study linkage of class I, II and III genes belonging to the human major histocompatibility (HLA) complex. The results establish that the class II DOβ and DZα genes are linked with the DP Subregion, centromeric to the DQ/DX-DR-C4 chromosomal segment, and allow us to estimate the minimal length of the entire HLA complex.
