The flare program uses a set of reference haplotypes to infer the ancestry of each allele in a set of admixed study samples. The flare program is fast, accurate, and memory-efficient.
Last updated: January 15, 2024
Current version: 0.5.1
- Installation
- Running flare
- Ancestry indices
- Output files
- Running flare with multiple chromosomes
- Running flare with small or large sample sizes
- Change log
- License
- Acknowledgments
- Citation
You can download the latest executable file, flare.jar, with the command:
wget https://faculty.washington.edu/browning/flare.jar
or you can download the source files and create the executable file with the commands:
git clone https://github.com/browning-lab/flare.git
javac -cp flare/src/ flare/src/admix/AdmixMain.java
jar cfe flare.jar admix/AdmixMain -C flare/src/ ./
jar -i flare.jar
The flare program requires Java version 1.8 (or a later version). Use of an earlier Java version will produce an "Unsupported Class Version" error.
The command:
java -jar flare.jar
prints a summary of the command line arguments.
To run flare, enter the following command:
java -Xmx[GB]g -jar flare.jar [arguments]
where [GB] is the maximum number of gigabytes of memory to use, and [arguments] is a space-separated list of parameter values, each expressed as parameter=value.
The shell script run.flare.test will run a test flare analysis.
The flare program has five required parameters. Two of the required parameters specify Variant Call Format (VCF) files. A VCF record may have multiple ALT alleles and must include a genotype (GT) FORMAT subfield. All genotypes must be phased and have no missing alleles. If a VCF file has unphased or missing genotypes, you can phase the genotypes and fill in the missing genotypes using the Beagle program. Any input file with a name ending in ".gz" is assumed to be gzip-compressed. Any input VCF file with a name ending in ".bref3" is assumed to be bref3-compressed. Software for bref3 compression and decompression can be downloaded from the Beagle web site.
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ref=[file] where [file] is the reference VCF file that contains genotype data for each reference sample. Flare will ignore samples in the reference VCF file that are not present in the reference panel file (see the ref-panel parameter).
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ref-panel=[file] where [file] is a reference panel file with two whitespace-delimited fields per line. The first field is a sample identifier in the reference VCF file (see the ref parameter), and the second field is the name of the reference panel containing the reference sample. Flare will ignore samples in the reference VCF file that are not present in the reference panel file. A reference panel should contain individuals from the same source population. A reference panel should not normally contain admixed samples.
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gt=[file] where [file] is the study VCF file containing genotype data for admixed study samples whose ancestry is to be inferred. The gt-samples parameter can be used to restrict the analysis to a subset of samples in the study VCF file. All admixed study samples in an analysis should be from the same population.
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map=[file] where [file] is a PLINK format genetic map with cM units. Positions of markers that are between genetic map positions are estimated using linear interpolation. The chromosome identifiers in the genetic map and the input VCF files must match. HapMap genetic maps in cM units are available for GRCh36, GRCh37, and GRCh38.
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out=[string] where [string] is the output filename prefix.
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array=[true/false] specifies whether the input data are from a SNP array. The min-mac parameter is ignored if array=true. By default, flare assumes the input data are sequence data (default: array=false).
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min-maf=[number < 0.5] specifies the minimum minor allele frequency in the reference VCF file in order for a marker to be included in the analysis (default: min-maf=0.005). For multi-allelic markers, the minor allele is the allele with the second-largest frequency.
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min-mac=[number ≥ 0] specifies the minimum minor allele count in the reference VCF file in order for a marker to be included in the analysis (default: min-mac=50). The min-mac parameter is ignored if array=true. If array=false, the min-mac parameter must be less than one-half the number of reference haplotypes. For multi-allelic markers, the minor allele is the allele with the second-largest frequency.
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probs=[true/false] specifies whether posterior ancestry probabilities are reported (default: probs=false). At each marker, the ancestry with the highest posterior probability for each haplotype is always reported in the output VCF file. If probs=true, posterior probabilities for each ancestry, haplotype, and marker will also be reported in the output VCF file. Reporting posterior probabilities will modestly increase memory use and computation time and significantly increase the size of the output VCF file.
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gen=[integer ≥ 1] specifies the number of generations since admixture (default: gen=10). If em=true, the specified gen parameter is an initial value for the gen parameter that will be used in the parameter estimation algorithm. The gen parameter is ignored if the model parameter is used.
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model=[file] where [file] is a whitespace-delimited file containing model parameters (see Model file format). If the model parameter is not used, flare will supply a reasonable set of model parameters (see the flare paper for details). If em=true (the default), flare will estimate the number of generations since admixture and the proportion of genotypes with each ancestry and will replace the values for these two parameters in the model file with their estimated values. The model parameters used in the analysis are reported in the output model file.
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em=[true/false] specifies whether the number of generations since admixture and the proportion of genotypes with each ancestry will be estimated using an iterative expectation maximization (EM) algorithm prior to inferring local ancestry (default: em=true).
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gt-samples=[file] (or gt-samples=^[file]) where [file] is a text file containing one sample identifier per line. Only admixed study samples that are present in [file] (or absent from [file] if [file] is preceeded by ^) will be analyzed. If the gt-samples parameter is omitted, all admixed study samples will be included in the analysis. The gt-samples parameter filters the study samples, and the ref-panel parameter filters the reference samples.
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gt-ancestries=[file] where [file] is a whitespace-delimited text file containing ancestry proportions for a set of samples. The gt-ancestries file has the same format as the output global ancestries file (see Global ancestries file format). If a study sample is present in the first column of the gt-ancestries file, the ancestry proportions in the gt-ancestries file will be used when estimating local ancestry in that sample; otherwise, study-wide ancestry proportions will be used.
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excludemarkers=[file] where [file] is a text file containing markers (one marker identifier per line) that are to be excluded from the analysis. A marker identifier can be an identifier from the VCF record ID field, or it can be a VCF record's CHROM and POS fields separated by a colon (i.e. "CHROM:POS").
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nthreads=[integer ≥ 1] specifies the number of computational threads to use for the analysis. The default nthreads parameter is the number of CPU cores. The nthreads parameter value is printed in the output log file.
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seed=[integer] specifies the seed for random number generation (default: seed=-99999). Repeating an analysis with the same seed and nthreads parameters will produce the same local ancestry estimates.
The flare program obtains the list of ancestries from the input files. If the model parameter is specified, flare will use the list of of ancestries at the start of the model file. If the model parameter is not specified, flare will use the reference panel names in the ref-panel file, in the order each name first appears in the ref-panel file, as the ancestry names.
If the gt-ancestries parameter is specified, the list of ancestries in the header line of the gt-ancestries file must have the same ancestries in the same order as the list of ancestries obtained from the model or ref-panel file.
The index of an ancestry in the list of ancestries determines a unique, non-negative integer associated with each ancestry. The first ancestry in the list has index 0, the second ancestry in the list has index 1, and so on.
The flare program produces four output files: a log file, a model file, a VCF file, and a global ancestry file.
The output log file (.log) contains a summary of the analysis.
The output model file (.model) contains the model parameters used in the analysis. The output model file has the same format as the optional input model file (see Model file format).
The output VCF file (.anc.vcf.gz) contains the phased input genotypes and the estimated local ancestry for each allele. The most probable ancestry at each marker for a admixed sample's first and second haplotype are reported in the AN1 and AN2 FORMAT subfields. If probs=true, the posterior ancestry probabilities at each marker for the admixed sample's first and second haplotypes are reported in the ANP1 and ANP2 FORMAT subfields. The integer that identifies each ancestry is given in the "##ANCESTRY=<...>" meta-information line.
The output global ancestries file (.global.anc.gz) contains the estimated global ancestry proportions for each admixed sample. The global ancestry file has the same format as the optional input gt-ancestries file (see Global ancestry file format).
A global ancestries file is a whitespace-delimited text file containing
the global ancestry proportions for a set of samples. If there are
SAMPLE, and the remaining fields
are the
A model file contains model parameters. The model file can contain comment lines, blank lines, and data lines. A comment line is a line whose first non-whitespace character is the '#' character. A blank line contains only whitespace characters. All other lines are data lines. Data lines contain whitespace-delimited fields that specify the model parameters.
If there are
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The first data line is the list of
$A$ ancestry names. The first ancestry in the list has index 1. -
The second data line is the list of the
$P$ reference panel names. The first reference panel in the list has index 1. -
The third data line is the number of generations since admixture.
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The fourth data line is a vector of length
$A$ whose$i$ -th element is the proportion of admixed sample genotypes with ancestry$i$ . -
The next
$A$ data lines contain the first$A \times P$ matrix. The$(i,j)$ -th element of the matrix is the probability that a model state haplotype is in reference panel$j$ when the model state ancestry is$i$ . -
The next
$A$ data lines contain the second$A \times P$ matrix. The$(i,j)$ -th element of the matrix is the probability that a model state haplotype and the admixed sample haplotype carry different alleles when the model state haplotype is in reference panel$j$ and the model state ancestry is$i$ . -
The final data line is a vector of length
$A$ whose$i$ -th element is the the rate of the exponential identity-by-descent segment cM-length distribution when the most recent common ancestor is pre-admixture and has ancestry$i$ .
It is not normally necessary to use a model file because flare will automatically estimate model parameters by default (see the em parameter). If you want to specify the model parameters, the easiest way to ensure that the model file is in the correct format is to run flare without the model parameter, and then modify the values in the output model file.
If an input VCF file contains multiple chromosomes, flare will estimate model parameters using data from the first chromosome and use these model parameters for all subsequent chromosomes in the VCF file.
If you analyze each chromosome separately, you can use the same model parameters for all chromosomes by analyzing one chromosome, and then analyze each remaining chromosome with em=false and the model parameter set equal to the output model file from the first chromosome's analysis.
If the sample size is too small for accurate estimation of model parameters, you can use the model and em=false parameters to specify the model parameters used in the analysis.
If you are analyzing an extremely large number of admixed samples and need to reduce memory use, you can partition the admixed samples into subsets and analyze each subset of admixed samples separately (see the gt-samples parameter). The inferred ancestry for a partitioned and a non-partitioned analysis will be the same if you specify em=false and use the same model, seed, and nthreads parameters for each analysis.
- Add a header line to the output global ancestries file (version 0.5)
- Add an optional gt-ancestries command line parameter (see Optional parameters) (version 0.5)
- Added global ancestries file with global ancestry probabilities (version 0.4)
- Add support for bref3-compressed VCF files (version 0.4)
The flare program is licensed under the Apache License, Version 2.0 (the License). You may obtain a copy of the License from https://www.apache.org/licenses/LICENSE-2.0
Thank you to Kai Zeng and Thomas Hickman for suggesting several of the new features in flare versions 0.4 and 0.5, and to Thomas Hickman for creating and sharing implementations of two features: support for bref3-compressed VCF files and for user-specified, per-sample admixture proportions.
If you use flare in a published analysis, please report the program version printed in the log file and cite the article describing the flare method:
S R Browning, R K Waples, B L Browning (2023). Fast, accurate local ancestry estimation with FLARE. The American Journal of Human Genetics 110(2):326-335. doi: http://dx.doi.org/10.1016/j.ajhg.2022.12.010
Sharon Browning developed the flare method.
Brian Browning developed the flare software.