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Meaning Of '0' Quality Score In Maq?

If a read has a zero quality score in MAQ does that mean:

a) The read aligns to multiple positions b) The read aligns to nowhere

I think it's either one or both of these but I'd hope someone can clear it up for me?

quality

1 answer

It means the reads map to multiple positions in this case - equally well.

And a quick check of the MAQ FAQ would have shown this:

"What happens to the reads that can be mapped to many positions?

If a read can be mapped to several equally best positions, Maq will randomly choose one position and give the alignment a zero mapping quality."

Oh right, dunno how I missed that, is there really any point in filtering these out if this is the case? I'm analyzing some rna-seq data.

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