Genomics: Deciphering the DNA Blueprint, Variant Discovery & Chromosomal Assemblies

🧬 Module 1: Biological Foundations of the Genome

🔬 Module 2: High-Throughput Sequencing Architectures

🖼️ Module 3: Visual Flowchart & Variant Spectrum

💻 Module 4: Production Computational Pipeline & Code

#!/usr/bin/env bash
set -euo pipefail

# ==============================================================================
# Production Germline Variant Discovery Pipeline (GATK Best Practices)
# Sample: NA12878 (Human Exome / WGS) | Reference: GRCh38.d1.vd1
# ==============================================================================
REF="/genomes/Homo_sapiens/GRCh38/GRCh38.fa"
DBSNP="/genomes/Homo_sapiens/GRCh38/dbsnp_146.hg38.vcf.gz"
MILLS_INDEL="/genomes/Homo_sapiens/GRCh38/Mills_and_1000G_gold_standard.indels.hg38.vcf.gz"
SAMPLE_ID="NA12878"
THREADS=16

echo "[Step 1] QC & Adapter Trimming with fastp..."
fastp \
  -i ${SAMPLE_ID}_R1.fastq.gz -I ${SAMPLE_ID}_R2.fastq.gz \
  -o ${SAMPLE_ID}_trimmed_R1.fastq.gz -O ${SAMPLE_ID}_trimmed_R2.fastq.gz \
  --detect_adapter_for_pe --thread ${THREADS} \
  --html ${SAMPLE_ID}_fastp.html --json ${SAMPLE_ID}_fastp.json

echo "[Step 2] BWA-MEM2 Reference Alignment & Read Group Addition..."
# RG: ID=Flowcell.Lane, SM=SampleName, PL=ILLUMINA, LB=Library1
bwa-mem2 mem -t ${THREADS} -M \
  -R "@RG\tID:H37VYDSX2.1\tSM:${SAMPLE_ID}\tPL:ILLUMINA\tLB:Lib_WES_01" \
  ${REF} ${SAMPLE_ID}_trimmed_R1.fastq.gz ${SAMPLE_ID}_trimmed_R2.fastq.gz | \
  samtools sort -@ 8 -m 2G -o ${SAMPLE_ID}_sorted.bam -

echo "[Step 3] Marking Duplicates with GATK MarkDuplicatesSpark..."
gatk MarkDuplicatesSpark \
  -I ${SAMPLE_ID}_sorted.bam \
  -O ${SAMPLE_ID}_dedup.bam \
  -M ${SAMPLE_ID}_dup_metrics.txt \
  --conf "spark.executor.cores=${THREADS}"

samtools index ${SAMPLE_ID}_dedup.bam

echo "[Step 4] Base Quality Score Recalibration (BQSR)..."
gatk BaseRecalibrator \
  -R ${REF} \
  -I ${SAMPLE_ID}_dedup.bam \
  --known-sites ${DBSNP} \
  --known-sites ${MILLS_INDEL} \
  -O ${SAMPLE_ID}_recal_data.table

gatk ApplyBQSR \
  -R ${REF} \
  -I ${SAMPLE_ID}_dedup.bam \
  --bqsr-recal-file ${SAMPLE_ID}_recal_data.table \
  -O ${SAMPLE_ID}_final_bqsr.bam

echo "[Step 5] HaplotypeCaller Variant Discovery (GVCF Mode)..."
gatk --java-options "-Xmx32g" HaplotypeCaller \
  -R ${REF} \
  -I ${SAMPLE_ID}_final_bqsr.bam \
  -O ${SAMPLE_ID}.g.vcf.gz \
  -ERC GVCF \
  --native-pair-hmm-threads ${THREADS}

echo "[Step 6] GenotypeGVCFs (Emit Final VCF)..."
gatk GenotypeGVCFs \
  -R ${REF} \
  -V ${SAMPLE_ID}.g.vcf.gz \
  -O ${SAMPLE_ID}_raw_variants.vcf.gz

echo "[Step 7] Hard-Filtering High-Confidence SNVs..."
gatk VariantFiltration \
  -R ${REF} \
  -V ${SAMPLE_ID}_raw_variants.vcf.gz \
  --filter-expression "QD < 2.0 || QUAL < 30.0 || SOR > 3.0 || FS > 60.0 || MQ < 40.0" \
  --filter-name "GATK_SNV_HARD_FILTER" \
  -O ${SAMPLE_ID}_filtered.vcf.gz

echo "Pipeline Finished Successfully: ${SAMPLE_ID}_filtered.vcf.gz ready for Ensembl VEP annotation."

🏥 Module 5: Real-World Clinical Case Study

Case: De Novo Dravet Syndrome Variant Discovery in an Infant with Intractable Seizures

Patient Presentation: An 8-month-old female infant presented with recurrent febrile and non-febrile tonic-clonic seizures refractory to standard anti-epileptic therapy. Brain MRI was unremarkable. Whole Exome Sequencing (WES, 100× target depth) was conducted across the patient and unaffected biological parents (Trio analysis).

Clinical Outcome & Actionability: Identification of the premature termination codon in SCN1A (encoding the alpha-1 subunit of voltage-gated sodium channel NaV1.1) established a definitive molecular diagnosis of Dravet Syndrome. Sodium channel-blocking drugs (e.g. carbamazepine, lamotrigine) were immediately contraindicated, and treatment was successfully transitioned to stiripentol and clobazam, reducing seizure frequency by >80%.

📦 Module 6: Essential Software Directory & Official Links

⚠️ Module 7: Bioinformatic Pitfalls & Quality Control Standards

📝 Module 8: Self-Assessment Exercises & Practice Datasets