What Is Score Bits In Blast?

Question

[Manju]

i want to konw that what does it mean score and bits in local blast output from the following example?'.

Score = 38.2 bits (19), Expect = 0.11
 Identities = 22/23 (95%)



Query: 1      cttaacttcagctacctcgagta 23
          <br>|||||||||||||||||| ||||<br>
Sbjct: 732552 cttaacttcagctacctccagta 732574

Answer 1

[Nikolay Vyahhi]

See this description of the bit score on NCBI.

Also from this NCBI page:

The bit score gives an indication of how good the alignment is; the higher the score, the better the alignment. In general terms, this score is calculated from a formula that takes into account the alignment of similar or identical residues, as well as any gaps introduced to align the sequences.

[Larry_Parnell]

Thank you, Nikolay, for the "obvious" answer. This is a legitimate question, of course, but could have easily been answered by Manju by simply looking at the extensive and useful help pages and other documentation provided on the NCBI pages.

Answer 2

[Larry_Parnell]

A bit is a measure of information content. Bites, like bytes, are units of measure for digital information, in this case, with regard to the alignment and hence the similarity of the two sequences.