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Tophat alignments is low but STAR is high.

If I used Tophat to align reads to human genome and I got ~72% alignment rate. Then I realigned the reads using STAR and around 90% of the reads were mapped. I also used the same commands of tophat to align another dataset and got 90% alignments rate. So I don't think I am not using tophat incorrectly.

I just used trimgalore before alignment . This confuses me. Can we have explanation?


tophat -p 4 --no-mixed -G genes.gtf --library-type fr-unstranded -o out genome reads_val_1.fq.gz reads_val_2.fq.gz


alignment rna-seq

2 answers

Tophat is an inferior and antiquated tool. Its inferiority has been born out in countless comparisons. You should never use tophat2 for new projects.

I think also I am using the default parameters of Star which could be the reason for the difference. 10 mismatches in Star vs 2 only in tophat. Also the softclipping default is high in Star vs no in tophat.

Sounds right. You can look at some reads that were mapped by STAR but not by tophat and see how many mismatches they have

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