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Old 10-08-2010, 01:37 PM   #1
Bio.X2Y
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Location: Europe

Join Date: Apr 2010
Posts: 46
Default Why are Illumina paired-end SRA datasets made up of 3 FASTQ files?

I'm looking at some NCBI SRA datasets for Paired-End Illumina Rna-seq.

In each case, the dataset is made up of 3 fastq files, even though I would only expect 2 (one for each end).

Example:

SRR018256.fastq (2,048,908 lines)
SRR018256_1.fastq (50,313,152 lines)
SRR018256_2.fastq (50,313,152 lines)

All files look OK, and the _1 and _2 files have the same number of lines, as I would expect.

Does anyone have any idea what the third file might be?

Thanks.
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