BLAST: Difference between revisions
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The results of a BLAST search give a graphic summary of the amount of [[Sequence alignment|alignment]] between the query sequence and the sequence hits from the database. The database sequences which produce significant allignments are shown in a table, which tells you the protein that the sequence codes for. Each has an accession number; clicking on this accession number allows you to see the souce organism of the protien, as well as giving links to papers on the protein. The E value ([[Expect vlaue|Expect value]]) is the staistical significance threshold; it gives the number of hits that are likely to be found by chance, therefore a lower E value will result in better matches as the probability of a chance result is less. | The results of a BLAST search give a graphic summary of the amount of [[Sequence alignment|alignment]] between the query sequence and the sequence hits from the database. The database sequences which produce significant allignments are shown in a table, which tells you the protein that the sequence codes for. Each has an accession number; clicking on this accession number allows you to see the souce organism of the protien, as well as giving links to papers on the protein. The E value ([[Expect vlaue|Expect value]]) is the staistical significance threshold; it gives the number of hits that are likely to be found by chance, therefore a lower E value will result in better matches as the probability of a chance result is less. | ||
The Blast web page can be found at: [http://blast.ncbi.nlm.nih.gov/Blast.cgi http://blast.ncbi.nlm.nih.gov/Blast.cgi] | |||
=== References === | |||
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Revision as of 12:19, 14 November 2011
BLAST is a primary sequence database that enables you to compare a DNA or protein sequence of interest to other known sequences, allowing you to find regions of similarity between them.[1] There are 5 different BLAST programmes depending on the type of sequence you are studying. The first, BlastP, allows you to compare an amino acid query sequence against a protein database. BlastN enables you to look at a nucleotide query sequence against a nucleotide sequence database. Using BlastX you can compare a nucleotide query sequence translated in all reading frames against a protein sequence database. With tBlastN you can see the similarites between a protein query sequence and nucleotide sequences from the database, dynamically translated in all reading frames, and finally, tBlastX allows you to compare the six-frame translations of a nucleotide query sequence against the six-frame transations of a nucleotide sequence database.[1]
The results of a BLAST search give a graphic summary of the amount of alignment between the query sequence and the sequence hits from the database. The database sequences which produce significant allignments are shown in a table, which tells you the protein that the sequence codes for. Each has an accession number; clicking on this accession number allows you to see the souce organism of the protien, as well as giving links to papers on the protein. The E value (Expect value) is the staistical significance threshold; it gives the number of hits that are likely to be found by chance, therefore a lower E value will result in better matches as the probability of a chance result is less.
The Blast web page can be found at: http://blast.ncbi.nlm.nih.gov/Blast.cgi