Editing Contig (section)

===Gaps between contigs===
Gaps often remain after initial BAC contig construction.  These gaps occur if the [[Bacterial Artificial Chromosome]] (BAC) library screened has low complexity, meaning it does not contain a high number of STS or restriction sites, or if certain regions were less stable in cloning hosts and thus underrepresented in the library.<ref name="contig assembly" />  If gaps between contigs remain after STS landmark mapping and restriction fingerprinting have been performed, the sequencing of contig ends can be used to close these gaps.  This end-sequencing strategy essentially creates a novel STS with which to screen the other contigs.  Alternatively, the end sequence of a contig can be used as a primer to [[Primer walking|primer walk]] across the gap.<ref name="textbook" />