/DNA-seq

DNA-seq Data process (example from real case)

0. Overview

DNA-seq：

  1. create an environment for DNA

    install trimmomatic, bwa, samtools and snakemake

  2. use trimming script

    $ vim sk_trim # to revise the script

    $ snakemake -j 8 -s sk_trim

Main process

  1. Quality assessment
  2. Alignment against GRCh38
  3. Duplicate removal
  4. Variant calling (germline or somatic mode)
  5. Variant annotation

1. Preparation

0.1 install Miniconda3 in Linux

cd /tempwork173/qiyoyou/
wget https://repo.anaconda.com/miniconda/Miniconda3-latest-Linux-x86_64.sh
bash Miniconda3-latest-Linux-x86_64.sh
source /home/qiyoyou/.bashrc

0.2 create an environment

conda create -n py3.7 python=3.7
source activate py3.7
deactivate

1.1 create an environment named 'DNA' and activate this environment

conda create -n DNA python=3.7
conda activate DNA

1.2 install 'fastqc', 'multiqc', 'trimmomatic', 'bwa', 'samtools' and 'snakemake' in DNA enviroment

conda install -c bioconda fastqc
conda install -c bioconda multiqc
conda install -c bioconda trimmomatic
conda install -c bioconda bwa
conda install -c bioconda samtools
conda install -c bioconda snakemake
conda install -c bioconda htslib ## for bgzip and tabix

2. Quality Check

2.1 Make sure you activate the enviromment since we installed 'fastqc' within and change direction to the folder containing raw .fastq data

conda activate DNA
cd /tempwork173/qiyoyou/Liu_WES_201903/RawData/

2.2 Quality check with 'fastqc'. Apply fastqc to all file with '.gz' pattern (It usually takes a lot of time if sequence data being large)

fastqc *.gz

2.3 Quality check with 'multiqc'. Apply multiqc to the output (.html) in this folder (./). This process integrate all the seperate output .html files into one.

multiqc ./

3. Quality trimming and adapter removal using TRIMMOMATIC (tentative)

[link to TRIMMOMATIC website]

4. Alignment against the GRCh38 reference assembly

[link to the search page of hg38]

4.1 Build a GRCh38 genome index (bwa)

Build a folder for storing the index and cd to this folder.

cd /tempwork173/qiyoyou/db/
mkdir grch38_bwa
cd grch38_bwa/

Download hg38 .fasta from the link and store it to this folder.

wget https://storage.cloud.google.com/genomics-public-data/resources/broad/hg38/v0/Homo_sapiens_assembly38.fasta?_ga=2.56607659.-1064644800.1560758967

Making bwa index

[link to bwa manual]

bwa index Homo_sapiens_assembly38.fasta

4.2 Use alignment script to perform align, SAM to BAM and stats

Remember to revise the script to adapt to your own filenames and path names via 'vim' command.

cd /tempwork173/qiyoyou/Liu_WES_201903/scripts/
vim sk_align
snakemake -j 8 -s sk_align   ## use 8 threads

5. Remove duplicate and mpileup

6. Variant calling (germline) with VarScan

[link to VarScan manual]

Here is a really flexible settings for those parameters. (parameters:--min-coverage 20 --min-var-freq 0.2 --min-reads2 4 --min-avg-qual 20 --p-value 0.05)

7. Variant annotation

7.1 Apply 'bgzip' and 'tabix' on .vcf file

cd /tempwork173/qiyoyou/Liu_WES_201903/calling/
parallel bgzip {} ::: *.vcf
parallel tabix -p vcf {} ::: *.vcf.gz

# or one by one
# For each VCF file:
bgzip Variants_sample_A.raw.vcf
tabix -p vcf Variants_sample_A.raw.vcf.gz

7.2 Create an folder and download VCFtools

[VCFtools download link]

cd /tempwork173/qiyoyou/
mkdir tools
cd tools/
tar -xvf vcftools_0.1.13.tar.gz

7.3 Go to the decompressed folder and merge all the .vcf.gz into one .vcf file

Merge seperate .vcf files into one via VCFtools:vcf-merge. After this procedure, 'Variants_all_samples.vcf' can be uploaded to wANNOVAR to perform functional annotation.

cd /tempwork173/qiyoyou/tools/vcftools_0.1.13/perl/
perl vcf-merge /tempwork173/qiyoyou/Liu_WES_201903/calling/temp/*.vcf.gz >| /tempwork173/qiyoyou/Liu_WES_201903/calling/temp/Variants_all_samples.vcf

7.4 Create a combined .vcf file without header by using 'awk' (optional)

Remove the header lines containing '##'.

awk '! /\##/' Variants_all_samples.vcf > Variants_all_samples_no_header.vcf

Supplementary

[How to Download hg38/GRCh38 FASTA Human Reference Genome]

Reference

(Analysis workflow)

  1. Lee CY, Chiu YC, Wang LB, et al: Common applications of next-generation sequencing technologies in genomic research. Translational Cancer Research 2013;2:33-45. http://tcr.amegroups.com/article/view/962/html