BioGem Blog

Biological sequence alignment is a method to find similarities between two sequences. The characters (letters or biological sequence alphabets) are arranged row-wise and column-wise according to match/identity and mismatch of characters through symbol representation. In row-wise, a gap character (hyphen symbol ‘-’) is used to align/adjust the sequence characters for matching without changing the order. Correspondingly, the column-wise characters such as match (same character, pipe symbol ‘|’, colon symbol ‘:’, asterisk symbol ‘*’, or dot symbol ‘.’), mismatch (anyone of the sequence character, or blank space ‘ ’), positive (positive symbol ‘+’), and gap/indel (blank space ‘ ’) are used to represent sequence alignment. A sequence or sequence alignment must be properly formatted in a text editor/word processor using fixed-width fonts to find the differences of characters in the s...

Basic Local Alignment Search Tool (BLAST) is a collection of programs developed using heuristic algorithm in C++ for comparing DNA, RNA, and protein sequences. The standalone command-line interface (CLI) of BLAST is named as BLAST+. The latest version of NCBI BLAST+ can be downloaded from the FTP server of NCBI ( ftp://ftp.ncbi.nih.gov/blast/executables/blast+/LATEST ). This is a simple tutorial for creating a custom database, accessing the database, and performing a sequence search using BLAST+. 1. Creating a Custom Database A nucleotide ( nucl ) or protein ( prot ) database can be created using -dbtype parameter in makeblastdb program. We can create two types of database using command-line below, Non-indexed Database: ./makeblastdb -in DBX.fasta -out DBX -dbtype prot Building a new DB, current time: 12/04/2020 10:10:06 New DB name: C:\NCBI\blast-2.6.0+\bin\DBX New DB title: DBX.fasta Sequence type: Protein Keep MBits: T Maximum file size: 1000000000B Adding sequences ...