[1]BLAST (Basic Local Alignment Search tools)

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How BLAST program works


Overview: Edit

BLAST is a service provided by the National Center of Biotechnology Information (NCBI). BLAST uses algorithm for calculating similarity between nucleic acids or protein sequences using sequences present in the database. A nucleotide or protein sequence is sent to BLAST server  to find and compare NCBI databases for a sequence that are related to the sequence of interest and a summary of the query matches are displayed. Some basic requirement to start the BLAST program include: finding appropriate BLAST program from arrays of several BLAST, enter query sequence, select database to search, run BLAST search, Analyze output and finally interpret E-values ( Tom Madden, 2003) .


Some uses of BLAST include: Identify unknown sequence,build a homology tree for a protein,map a sequence in genome, and get clues about protein structure by finding similar proteins with known structures.

How BLAST program works Edit

NCBI Blast Tutorial

NCBI Blast Tutorial

On the (National Center for Biotechnology Information)web page, click BLAST on the right upper menu.There are five BLAST searches: nucleotide blast, protein blast, and three translated blasts (blastx, tblastin and tblastx). Generally, if starting with a DNA nucleotide sequence, the appropriate BLAST to use is the nucleotide blast. The

BLAST Results- Expect Values, part 1

BLAST Results- Expect Values, part 1

BLAST Results- Expect Values, part 2

BLAST Results- Expect Values, part 2

BLAST- New Results Format, Oct 2012

BLAST- New Results Format, Oct 2012

nucleotide blast uses nucleotide query to search a nucleotide database; and a protein sequence, uses protein query to search protein database. The results of BLAST search is displayed in three different categories: graphical representation, description columns, and  query sequence alignment.The E-values decreases exponentially with the Score (S) that that is assigned to the sequences that match. The lower the E-values within a range of 0 to 10-4 the more significant E-values and can be considered related or homologous to the starting sequence. And the higher the Score (S),the better the alignment ( Tom Madden, 2003).

References Edit

"BLAST Results: Expect Values, Part 1." YouTube. YouTube, 1 Oct. 2012. Web. 8 Sept. 2014

Madden, Tom. "Chapter 16 The BLAST Sequence Analysis Tool." The NCBI Handbook. 2nd ed. Bethesda, Md.: National Library of Medicine, 2002

"NCBI Blast Tutorial." YouTube. YouTube, 1 Oct. 2012. Web. 8 Sept. 2014

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