lower case bases in Velvet assembly

Question

[Tm]

Can any one tell me, what these lower case bases mean in assembled sequences (contigs.fa) obtained from velvet assembler.

For example:

>NODE_6732_length_139_cov_108.179855 AAGAGACTACATCTGATAAAGCAGATGCAATATGTTTCTATTTTGCTTGGTTTACAAGAT TTGCCGTAAAATTCCCATCAACTTCAGCACTTGGAAAGCAGTATGACAAGGTTAGGGAAA CTTATCTAAAATTCTATCAAAAATCATCAAAAata

I am working with Illumina single end (SE) reads and command which I used was as follows:

./velveth out_dir_velveth 17 -short -fastq input.fq

./velvetg out_dir_velveth -exp_cov auto -cov_cutoff auto -unused_reads yes -clean yes

Best,

Answer 1

[Kevin Blighe]

Hello,

In velvet, the lower-case bases define regions that have lower coverage. One would assume that high/low coverage is defined by the -cov_cutoff command-line parameter.

To add further for anyone else arriving here from a search engine for possibly related issue, 'N' bases represent gaps in the contigs, with the number of N bases in sequence representing the estimated size of the gap.

Kevin

[Tm]

Thanks Kevin,

You made it very much clear to understand.

Cheers, Toral