In my NGS data analysis, before mapping, I trimmed low-quality bases (<Q20) from 3' ends until a high quality (≥Q20) base appears. After that, I plotted the distribution of read length and obtained the weird periodical read length distribution. Please see attached.
In the graph, length distributions from different lanes or tiles were drawn in different colors. Frequencies of reads were oscillated with 5bp intervals.
I also saw this kind of weird length distribution for other our RNA-seq and genome sequence dataset, and RNA-seq data from SRA as well.
Does anyone know the reason why such periodical length distribution was appeared after trimming?
Thanks in advance.
In the graph, length distributions from different lanes or tiles were drawn in different colors. Frequencies of reads were oscillated with 5bp intervals.
I also saw this kind of weird length distribution for other our RNA-seq and genome sequence dataset, and RNA-seq data from SRA as well.
Does anyone know the reason why such periodical length distribution was appeared after trimming?
Thanks in advance.
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