About FASTQ sequence read files


Our sequence files are distributed in FASTQ format. Some are hosted on our own FTP site and some by the sequence read archive.


We use Sanger style phred scaled quality encoding.

The files are all gzipped compressed and the format looks like this, with a four-line repeating pattern

@ERR059938.60 HS9_6783:8:2304:19291:186369#7/2

Files for each individual

Many of our individuals have multiple fastq files. This is because many of our individual were sequenced using more than one run of a sequencing machine.

Each set of files named like ERR001268_1.filt.fastq.gz, ERR001268_2.filt.fastq.gz and ERR001268.filt.fastq.gz represent all the sequence from a sequencing run.

The labels with _1 and _2 represent paired-end files; mate1 is found in a file labelled _1 and mate2 is found in the file labelled _2. The files which do not have a number in their name are singled ended reads, this can be for two reasons, some sequencing early in the project was singled ended, also, as we filter our fastq files as described in our README if one of a pair of reads gets rejected the other read gets placed in the single file.

When a individual has many files with different run accessions (e.g ERR001268), this means it was sequenced multiple times. This can either be for the same experiment, some centres used multiplexing to have better control over their coverage levels for the low coverage sequencing, or because it was sequenced using different protocols or on different platforms.

For a full description of the sequencing conducted for the project please look at our sequence.index file

Related questions:

How do I find specific sequence read files?


The easiest way to find the sequence files you’re looking for is with the Data Portal. You can search for individuals, populations and data collections, and filter the files by data type and technologies. This will give you locations of the files, which you can use to download directly, or to export a list to use with a download manager.

Related questions:

What are your filename conventions?


Our filename conventions depend on the data format being named. This is described in more detail below.


Our sequence files are distributed in gzipped fastq format

Our files are named with the SRA run accession E?SRR000000.filt.fastq.gz. All the reads in the file also hold this name. The files with _1 and _2 in their names are associated with paired end sequencing runs. If there is also a file with no number it is name this represents the fragments where the other end failed qc. The .filt in the name represents the data in the file has been filtered after retrieval from the archive. This filtering process is described in a README.


Our variant files are distributed in vcf format, a format initially designed for the 1000 Genomes Project which has seen wider community adoption.

The majority of our vcf files are named in the form:


This name starts with the population that the variants were discovered in, if ALL is specifed it means all the individuals available at that date were used. Then the region covered by the call set, this can be a chromosome, wgs (which means the file contains at least all the autosomes) or wex (this represents the whole exome) and a description of how the call set was produced or who produced it, the date matches the sequence and alignment freezes used to generate the variant call set. Next a field which describes what type of variant the file contains, then the analysis group used to generate the variant calls, this should be low coverage, exome or integrated and finally we have either sites or genotypes. A sites file just contains the first eight columns of the vcf format and the genotypes files contain individual genotype data as well.

Release directories should also contain panel files which also describe what individuals the variants have genotypes for and what populations those individuals are from.

Related questions: