![]() The assembly software then searches this database for pairs of overlapping reads. The subsequent sequence reads, which are the data that contain the sequences of the small fragments, are put into a database. In bottom-up sequencing projects, amplified DNA is sheared randomly into fragments appropriately sized for sequencing. Because current technology allows for the direct sequencing of only relatively short DNA fragments (300–1000 nucleotides), genomic DNA must be fragmented into small pieces prior to sequencing. The bottom-up DNA sequencing strategy involves shearing genomic DNA into many small fragments ("bottom"), sequencing these fragments, reassembling them back into contigs and eventually the entire genome ("up"). This meaning of contig is consistent with the original definition by Rodger Staden (1979). Sequence contigs Ī sequence contig is a continuous (not contiguous) sequence resulting from the reassembly of the small DNA fragments generated by bottom-up sequencing strategies. The gel readings in a contig can be summed to form a contiguous consensus sequence and the length of this sequence is the length of the contig. All gel readings belong to one and only one contig, and each contig contains at least one gel reading. A contig is a set of gel readings that are related to one another by overlap of their sequences. In 1980, Staden wrote: In order to make it easier to talk about our data gained by the shotgun method of sequencing we have invented the word "contig". Contigs can thus refer both to overlapping DNA sequences and to overlapping physical segments (fragments) contained in clones depending on the context. In bottom-up sequencing projects, a contig refers to overlapping sequence data ( reads) in top-down sequencing projects, contig refers to the overlapping clones that form a physical map of the genome that is used to guide sequencing and assembly. For the contig defragmentation program, see Contig (defragmentation utility).Ī contig (from contiguous) is a set of overlapping DNA segments that together represent a consensus region of DNA. ![]() This article is about contig in DNA sequencing.
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