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== Cóntigo de secuencia ==
Un cóntigo de secuencia é unha secuencia continua (non contigua) resultante da reensamblaxe dos pequenos fragmentos de ADN xerados por estratexias de [[secuenciación shotgun|secuenciación de abaixo a arriba]]. Este significado de cóntigo é consistente coa definición orixinal que lles deu [[Rodger Staden]] (1979).<ref>{{cite journal |author=Staden R |year=1979 |title=A strategy of DNA sequencing employing computer programs |journal=Nucleic Acids Research |volume=7 |pages=2601–2610 |pmc=327874 |pmid=461197 |doi=10.1093/nar/6.7.2601}}</ref> A estratexia de [[secuenciación do ADN]] de abaixo a arriba implica romper o
Today, it is common to use [[DNA sequencing theory#Pairwise end-sequencing|paired-end sequencing]] technology where both ends of ''consistently sized'' longer DNA fragments are sequenced. Here, a contig still refers to any contiguous stretch of sequence data created by read overlap. Because the fragments are of known length, the distance between the two end reads from each fragment is known.<ref name="pet">{{cite journal |vauthors=Fullwood MJ, Wei C, Liu ET |title=Next-generation DNA sequencing of paired-end tags (PET) for transcriptome and genome analyses |journal=Genome Research |year=2009 |volume=19 |pages=521–532 |doi=10.1101/gr.074906.107 |pmid=19339662 |issue=4|display-authors=etal}}</ref> This gives additional information about the orientation of contigs constructed from these reads and allows for their assembly into '''scaffolds'''. [[File:PET contig scaffold.png|thumb|Overlapping reads from paired-end sequencing form contigs; contigs and gaps of known length form scaffolds.]] Scaffolds consist of overlapping contigs separated by gaps of known length. The new constraints placed on the orientation of the contigs allows for the placement of highly repeated sequences in the genome. If one end read has a repetitive sequence, as long as its [[mate pair]] is located within a contig, its placement is known.<ref name="pet" /> The remaining gaps between the contigs in the scaffolds can then be sequenced by a variety of methods, including PCR amplification followed by sequencing (for smaller gaps) and [[Bacterial artificial chromosome|BAC]] cloning methods followed by sequencing for larger gaps.<ref name="textbook" />
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