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Old 01-29-2013, 02:18 AM   #1
Jluis
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Default Resequencing & variant calling issue

Dear all,

I have to analyze a set of samples that come from a re-sequencing project.
I've been given the coordinates where the genes under analysis (those I should carry out a variant calling analysis on) are located.
Since there are reads that map spuriously to other places in the ref. genome (due to the DNA amplification process), I need to figure out a way to extract only the reads that map to the coordinates I was informed previously.
-Can anybody tell me about any tool or R package able to perform this reads filtering?
-Can the filtering step be avoided by any means (e.g. passing the coordinates to a program that would later do de variant calling without the reads filtering step).?
-Any suggestions about which software I should use to do the variant calling after that filtering (Samtools, GATK, or any other you may know about?

Thanks in advance

JL
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Old 01-29-2013, 02:46 PM   #2
swbarnes2
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You can use BEDTools to filter a .bam based on a .bed file of target coordinates.

So align everything to the whole genome, for best accuracy, then filter for the reads that hit your targets.
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Old 01-30-2013, 06:18 AM   #3
Jluis
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@ swbarnes2, thank you very much for your kind help.
I'd like to ask you a question about bedtools if I may. I've been reading the description of the different bed-tools (http://bedtools.readthedocs.org/en/l...ols-suite.html) but I've been unable to find one that fits the excat functions you suggested. The most similar one (to my understanding) was the "intersect" tool but still doesn't seem to do the filtering you told me about. So, would you please tell me the name of the specific bed-tool you suggested me to use.

Thanks in advance

JL
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Old 01-30-2013, 08:30 AM   #4
swbarnes2
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I use intersect on exome capture data all the time. You give it a .bam file and a .bed of target regions, and it gets rid of reads that don't intersect the .bed regions.

If that's not what you want, then I don't get your question.
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Old 01-31-2013, 12:47 AM   #5
Jluis
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Dear swbarnes2,

You're right in everything, the program I need is intersectBed. I got it wrong because I didn't understand its functions from the online instructions I referred to yesterday. I've downloaded the Bedtools manual pdf and re-read it, and I found that intersectBed was the tool you were talking about (as you made clear in your previous answer). It seems to be exactly what I need.

Thank you very much

JL

Last edited by Jluis; 01-31-2013 at 03:08 AM. Reason: syntaxis
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Old 02-05-2013, 02:12 AM   #6
Jluis
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@swbarnes2

I've followed your instructions and then included another couple of steps to perform the whole (to my lack of experience with this particular analysis) study.

Do you consider this a proper workflow for a vcf analysis or do you think there's some missing step on it?

-Reads Mapping
-Bedtools Intersect to extract mapped regions of interest
-SNP/Indels calling using samtools mpileup/bcftools view and bcftools view/vcf utils

Thanks in advance for your advice
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