All sequences either 159 or 151 bp, normal? Illumina Novaseq6000

I have received fasta files from a vendor. They claim that the sequences should be 150 bp. I checked all sequences with FastaQ amd MultiQC and found that in any given fasta file, the sequences are either all 159 bp or in some files all 151 bp long. This is paired end from Illumina. Just wondering, is this normal? I am struggling a bit how to formulate the question. I think my question is, why are not all sequences exactly 150 bp as expected? If it is a different number, why are they not all of that different length, either all 159 or 151? This is from Illumina

Hi @neocat ,
I suggest discussing this with the sequencing service — they would know best what is normal with their service. The read length for Novaseq6000 depends on the flow cell that is used. Neither 151 bp nor 159 bp is normal, but the sequencing service would be best equipped to explain.

Good luck!

1 Like