Hi Jeremy,

Thank you very much for the reply. I have some more questions of the same topic.

1) My reads are 36nt long. How much should I set for "the Minimum length of 
reads segments" to get the most reliable output with the highest mapping of 
splicing junctions?. In my previous run of TopHat, I set it as 18. Can I reduce 
it more to get better mapping on splicing junctions?

2) I do not understand exactly how TopHat works as for the "Anchor length" 
although I have read the manual for TopHat.

Suppose I set the "Anchor length as 8 and the "Maximum number of mismatch that 
can appear in the anchor region of spliced alignment" as 0 when I run Tophat. 
Does it mean, for a read maps on two adjacent exons, TopHat will report this 
alignment to the outputs ".accepted hits" and ".splicing junctions" if either 
end of the read has 8 or more nucleotides mapping on one exon?

3) Is there disadvantage/negative effect if I choose to set the "Anchor length" 
at the lowest, for example 3? My understanding is that, under the 0 mismatch 
condition, if 3 nuceoides of one end of a read mapped on one exon, the other 
part of the read will map on the adjacent exon (in my case, the other part 
would be 33 nucleotides). So my understanding is that setting the "Anchor 
length" at 3 does not increase the inaccuracy of the alignment. Am I correct?



From: Jeremy Goecks [jeremy.goe...@emory.edu]
Sent: Tuesday, April 09, 2013 1:57 PM
To: Du, Jianguang
Cc: galaxy-user@lists.bx.psu.edu
Subject: Re: [galaxy-user] Are reads of 36nt in length long enough to accutatly 
map on splicing junctions?

In addition to reducing the "the Minimum length of reas segments", do I also 
need to reduce "Anchor length" to get more mapping on splicing junctins?

Definitely worth a try.

Looks like the setting for "Anchor length" only affects the number of mapped 
splicing junctions reported in the .splicing junctions output. Is my 
understanding correct?

No, it will affect mapped reads as well.

Does the "regions" mean the number of mapped splicing junctions?


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