DNA BLAST Results
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By now you should have the BLAST results back and open in another window.
We will now look at the results. The general layout, and the way the data is displayed should now be fairly familiar to you. However, we will:
  1. look at the different results sections
  2. examine the graph
  3. look at the sequence table
  4. look at, and interpret the alignment
The BLAST images below are taken from a search run on Sunday October 14, 2018 at 1:15:59 pm.
The DNA BLAST results - page header
The page header is always worth a glance if only to make sure you ran the right program and the right database was searched.
Top of the BLAST result page
1) What is the length of the nucleotide used for the search?
One answer only.
   2386
   3246
   3268
   3286
   3296
   4286
   4386
The DNA BLAST results - the graph
The graph gives an overview of the results returned and an indication of the degree of match. Moving your mouse over the graph will show the name of the DNA (although this appears to have stopped working). If you click on a line, a pop up will appear with additional information on the sequence.
The BLAST graph - the graph shows the degree of match between your sequence and sequences in the database
The DNA BLAST results - the table
The BLAST table - the table shows the matches along with links to the full database entry and alignment. The top hit is the best match.
The BLAST table shows the hits ordered by best to worse.
1) In the above figure (not your results) what is the accession number of the top DNA hit?
One answer only.
   AF089138
   AF099138
   AF099183
   AF099318
   AF099333
   AG099438
   FA099138
2) The E value of 0.0 for the first sequence in the above table shows that
One answer only.
   it is a very poor match.
   the DNA has not been fully sequenced.
   the DNA is unique in the database.
   there are no mismatches.
   it is a good hit.
   all mismatches are conserved.
The DNA BLAST results - the alignment
The alignment must be examined. Just because a DNA is listed in the table, it does not mean it is a good match. Below are two alignments.
The first alignment shows a very good (in fact exact) match.
Part of the top DNA alignment for a search run on as dated at the top of the page. Note that this is an exact match. The identities score is 100%, and and that there are no gaps.
1) In the above figure (not your results) what is length of the sequence retrieved from the database?
One answer only.
   3286
   3306
   3316
   3326
   3336
   3346
   3356
   3365
2) The above alignment is...
One answer only.
   global
   local
This alignment is not so good (this was taken from further down the list of alignments).
The above sequence alignment is the last one in the list and shows a poorer quality match.
 
1) The query sequence is
One answer only.
   the sequence that you sent to the database for comparison.
   the sequence retrieved for the database.
2) The 'Sbjct' sequence is
One answer only.
   the sequence that you sent to the database for comparison.
   the sequence retrieved for the database.
3) Were any gaps inserted to get the alignment in the above figure?
One answer only.
   No
   Yes
4) A '|' in the middle row of a DNA blast search shows
One answer only.
   that the bases matched.
   that the bases did not match.
   means that there was a conserved substitution.
5) A space ( ) in the middle row of a DNA blast search shows
One answer only.
   that the bases matched.
   that the bases did not match.
   means that there was a conserved substitution.
6) Like protein search alignments, DNA sequence alignments can also have conserved substitutions
One answer only.
   False
   True
So far we have:
  1. carried out a DNA BLAST search
  2. looked at the returned results
  3. examined the sequence alignments
We will now look at how to retrieve more information from the BLAST result...
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