Understanding BLAST Results for Sequence Alignment

BLAST (Basic Local Alignment Search Tool) is a widely used software for comparing a query sequence with a large database of sequences and finding the best matching sequences. The output of BLAST results provides information about the quality and significance of the sequence alignment between the query and the database sequences. Understanding the BLAST results is essential for interpreting the results and making informed conclusions about the query sequence and its relationship to other sequences in the database. You can use this facility here, NCBI BLAST Server


The BLAST results contain several sections that provide different types of information. Let’s take a look at each of them:

Query sequence information: This section includes information about the query sequence, such as its length, number of mismatches and gaps, and the percent identity between the query and the subject sequence. 


Hits list: This section lists the best matching sequences in the database, ranked by the E-value (expected value), which is a measure of the significance of the alignment. The hits list also provides information about the length of the matching sequences, the percent identity, and the number of gaps and mismatches. You can find it on the right side of the main result page produced by BLAST web server.

Alignment: This section provides a detailed view of the sequence alignment between the query and the subject sequence. It displays the matching and non-matching regions of the sequences and highlights the regions of the query and subject that are most similar.



Statistics: This section provides information about the search parameters used in the BLAST analysis, including the size of the database, the number of sequences searched, and the gap penalties used in the alignment.

Graphics: This section provides graphical representations of the sequence alignment, such as a dot plot or a histogram, which can help visualize the similarity between the query and subject sequences.

In conclusion, BLAST is a powerful tool for comparing sequences and finding the best-matching sequences in a database. Understanding the BLAST results is essential for interpreting the results and making informed conclusions about the query sequence and its relationship to other sequences in the database. By taking the time to understand the different sections of the BLAST results, you can gain a deeper understanding of your sequences and make more informed conclusions about their relationships to other sequences in the database.

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