Questions tagged [trimming]

To cut from the end. Trimming is often done on raw Illumina reads to discard low-quality bases or adapter sequences. Questions related to trimming algorithms, when, how to trim, trimming software.

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What are the right parameters to trim a small RNA transcriptome with trimmomatic?

I'm having some problems with finding the right parameters to trim my small RNA Illumina reads (51 nt long) with Trimmomatic. Before trimming, one of the samples (21M reads) looks like this: So for ...
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2answers
150 views

Is there a safe catch-all adapter sequence for trimming?

I would like to trim/mark adapters using trimmomatic or picard MarkIlluminaAdapters from a series of Illumina Paired-End read fastqs. The fastq files may have been done using different kits or ...
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3answers
96 views

Tools for quality trimming at 5 prime?

I'm looking for a tool that is capable to do quality trimming at 5' end and it is configurable. For example, I can choose the quality trheshold, the read length, etc. Any recommendations? I'm ...
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2answers
248 views

“Sequence Duplication Levels” module still fails after pre-processing Illumina data

I want to ask about why the sequence duplication levels are high after I trimmed by using Trimmomatic? I am using the following Trimmomatic operations: ...
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1answer
149 views

Demultiplexing and preprocessing for custom single-nucleus Drop-seq data

I am trying to reproduce the preprocessing of paired-end sequencing reads in Lake et al. (ref. 1). First, paired-end reads were filtered out if read 1 had more than four non-T bases in the last ten ...
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3answers
641 views

Why does cutadapt remove low quality bases from the ends of reads only?

I use cutadapt to remove low quality bases from my Illumina reads. The algorithm only removes low quality bases from the end until it reaches a good quality base. If there is a bad quality base beyond ...
6
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1answer
496 views

How to trim adapter sequences from GSE65360 in order to map the reads?

I am trying to map single-cell chromatin accessibility data from doi:10.1038/nature14590, obtained using scATAC-seq, to the reference genome. Example paired-end reads are here. The reads contain ...
8
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1answer
577 views

FASTQC overrepresented sequences after trimming

I have a set of RNA-seq samples from different experiments (Single and Paired End, depending on the experiment). I ran FASTQC in all the samples and found overrepresented adapter sequences: I removed ...
4
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1answer
245 views

insert size pre and post trimming

I have a problem here with my rna seq data: Sequencing details: rRNA was removed, followed by cDNA preparation and generation of stranded libraries using the TruSeq Stranded Total RNA Sample Prep ...
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4answers
289 views

How can I systematically detect unknown barcode/adapter sequences within a set of samples?

I have often downloaded datasets from the SRA where the authors failed to mention which adapters were trimmed during the processing. Local alignments tend to overcome this obstacle, but it feels a ...