In shotgun DNA sequencing projects, a contig (from contiguous) is a set of overlapping DNA segments derived from a single genetic source. A contig in this sense can be used to deduce the original DNA sequence of the source. This meaning of contig is in accordance with the original definition by Staden [1979].

A contig map depicts the relative order of a linked library of contigs representing a complete chromosome segment.

Semantic drift

The word contig is sometimes used to refer to one segment of a contig in the original sense.

A contig is also sometimes defined as the DNA sequence reconstructed from a set of overlapping DNA segments.

Fragmentation of a contig into 1-2kb pair segments provide suitable sized DNA segments for sequencing.

Special software must be used to assemble the segments back to one single un-interrupted piece (contig).

References

Staden,R. "A strategy of DNA sequencing employing computer programs", Nucleic Acids Res. 7, 2601-2610, (1979).