BLASTlike

BLASTlike denotes a class of sequence similarity search tools that adopt the seed-and-extend heuristics popularized by BLAST. They are designed to rapidly identify local regions of similarity between a query sequence and a large sequence database by trading exactness for speed.

The typical workflow includes constructing an index of short words (seeds), scanning the database for seed matches, extending matches locally in an ungapped or gapped fashion, and reporting high-scoring local alignments with associated statistics such as the bit score and E-value. Low-complexity regions are commonly masked or filtered to reduce spurious matches. The approach emphasizes speed and scalability, particularly for large genomic databases, at the cost of some sensitivity compared with exhaustive methods.

BLASTlike tools include the BLAST family (BLASTN, BLASTP, BLASTX, TBLASTN, TBLASTX). Variants such as PSI-BLAST perform iterative searches using a position-specific scoring matrix to improve sensitivity for distant homologs. MegaBLAST (often written as MegabLAST) is optimized for closely related sequences and rapid database searches, while Discontiguous MegaBLAST expands sensitivity for more divergent relationships by using spaced, non-contiguous word matches. Other tools in the broader ecosystem apply similar seed-and-extend strategies with different optimizations or scoring schemes.

In practice, BLASTlike methods are faster than exact alignment approaches but may miss some true positives due to their heuristic nature. They remain a foundational tool for functional annotation, homology detection, and initial genome analyses, widely available in public tool suites and online services.