Restriction endonuclease digestion of PCR products. (A) A fragment spanning exons 3 and 4 and the flanking introns was PCR amplified and digested with the restriction endonuclease Mlu I before electrophoresis on a 2% agarose gel, Southern blotted, and probed with the FVII cDNA sequence. Lane 1, normal control; lane 2, affected child, IV.2; lane 3, father, III.5; lane 4, mother, III.6. (B) Diagrammatic representation of the fragment the Mlu I sites are indicated.