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Bayesian haplotype-based genetic polymorphism discovery and genotyping.

freebayes is a Bayesian genetic variant detector designed to identify small polymorphisms, including SNPs, indels, MNPs, and complex events, using short-read sequencing data. It uses a haplotype-based approach, calling variants based on the literal sequences of reads aligned to a target, rather than precise alignment. This addresses the issue of multiple possible alignments for identical sequences. The tool takes BAM files (Phred+33 encoded quality scores) from multiple individuals and a FASTA reference genome to determine the most probable combination of genotypes at each reference position, outputting polymorphic positions in VCF format. It can utilize prior information from input VCF files and copy number variant maps (BED) to account for non-uniform ploidy variation. Freebayes is parallelizable using the freebayes-parallel wrapper, leveraging GNU parallel to process different genomic regions concurrently.
freebayes is a Bayesian genetic variant detector designed to identify small polymorphisms, including SNPs, indels, MNPs, and complex events, using short-read sequencing data.
Explore all tools that specialize in genotyping. This domain focus ensures freebayes delivers optimized results for this specific requirement.
Calls variants based on the literal sequences of reads, not just alignments, avoiding alignment-based biases.
Generates GVCF output, providing coverage information for non-called sites, useful for downstream filtering and annotation.
Allows specification of ploidy, accommodating variations in sample copy number.
Can be parallelized using `freebayes-parallel` script, distributing the analysis across multiple cores or nodes.
Uses an input VCF file to force calls at particular alleles, useful for targeted variant analysis.
Install freebayes using a pre-built binary or build from source.
Obtain a FASTA reference sequence and BAM-format alignment file.
Sort the BAM file by reference position.
Run freebayes with the reference and alignment files as input: `freebayes -f ref.fa aln.bam > var.vcf`.
Optionally, use parameters like `--gvcf` for coverage information, `--skip-coverage` to exclude high-coverage regions, or `-r` to specify a genomic region.
For parallelization, use the `freebayes-parallel` script.
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"Generally well-regarded for its haplotype-based approach and flexibility, but can be slow without parallelization."
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