Heteroduplex DNA formation in the recombinants. A subset of recombinants generated with the (A) Esp3I-cut, (B) Eco47III-cut, and (C) SpeI-cut enhancer-trap vectors in which the Cμ-region marker patterns are consistent with formation of hDNA is shown. In the recombinants, minimum tracts of hDNA are indicated by enclosure of relevant Cμ-region marker positions in rectangles. Marker positions that are deemed to reside in symmetrical hDNA are shaded. U, unidirectional hDNA; S, symmetrical hDNA; B, bidirectional hDNA.