Figure 4

Experimental validation of Southern blot probes. Each lane on the four blots A-D contains mouse genomic DNA extracted from a separate embryonic stem (ES) cell line, that was restriction-digested and size-separated on an 0.6% by gel electrophoresis before blotting. The gel was run for 16-18 hr at 20-22 V, and a molecular weight standard of HindIII-digested Lambda DNA was employed. Panels A-D were hybridized with probes designed against four distinct mouse loci situated near the Iqsec1, Igsf9, Iqsec3 and Gda genes in order to confirm whether homologous recombination had taken place, ablating or modifying the gene's function. In each case examples of wild-type (WT) and gene-targeted (TGT) DNA are revealed by the presence of the extra band in the TGT ES clones, at a differing molecular weight.