Long-range mapping of the transgenic human β globin locus by PFGE. YAC and transgenic mouse genomic DNA samples were digested with Sfi 1, resolved by PFGE, blotted, and probed with the 5′ 3.3 RI probe (A), β globin gene probe (B), and 3′ 3D probe (C). Lanes 1A and 1B and lane 2C, total chromosomal DNA from yeast strain YPH148. The 90-kb and 1,050-kb chromosomes from this strain cross-hybridize with plasmid sequences and provide useful markers. Lane 2A, partial Sfi 1 digest of the A85D10 YAC. Lane 1C, undigested total yeast DNA from YAC clone A201F4 provides a 150-kb marker. Lanes A85.62, A85.68, and A85.73 indicate Sfi 1–digested murine genomic DNA from each of the YAC transgenic lines described.