Basic Local Alignment Search Tool
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It is a program or an algorithm for searching and comparing primary biological sequence information, which is developed and maintained by a group at National Centre for Biotechnology Information (NCBI).
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The example of primary biological sequences is the amino acid sequences of different protein or the nucleotide of DNA sequence.
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There are different types of BLAST:
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BLASTP which searches a protein database.
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BLASTN to search a nucleotide database.
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TBLASTN which searches for a protein sequence in a nucleotide database by translating nucleotide sequences in all 6 reading frames.
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BLASTX which can search for a nucleotide sequence against a protein database by translating the query via all 6 reading frames.
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Gapped-BLAST
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psi-BLAST
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BLAST locates patches of regional similarity instead of calculating the best overall alignment using gaps.
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The program then uses a scoring matrix to rank these matches as positive, negative or zero. If the initial match is scored highly, the search is expanded in both directions until the ranking score falls off.
