Pop-Con: a tool to visualize genotype profiles on Site Frequency Spectrum from populational genomics data
Pop-Con is a tool designed to visualize genotype profiles of a Site Frequency Spectrum (SFS) from a Variant Calling Format (VCF) file  for SNP and indel variant. We define a genotype profile as the list of genotypes for all individuals at a given site. For example, "0/1,1/1,0/1,0/1" is the genotype profile corresponding to the VCF line below:
Dst_b1v03_scaf00008 54329 . G A 1970.68 PASS AC=6;AF=0.500;AN=12;BaseQRankSum=-6.140e-01;ClippingRankSum=0.00;DP=144;ExcessHet=4.8280;FS=6.723;MLEAC=5;MLEAF=0.417;MQ=60.00;MQRankSum=0.00;QD=15.28;ReadPosRankSum=-8.460e-01;SOR=0.440 GT:AD:DP:GQ:PL 0/1:16,22:38:99:558,0,409 1/1:1,11:12:3:309,3,0 0/1:26,28:54:99:750,0,617 0/1:8,11:19:99:286,0,203
Where individuals 1, 3 and 4 are heterozygote ("0/1") and individual 3 is homozygote for the alternative allele ("1/1") for this site.
Pop-Con takes as input a VCF file and uses the cyvcf2 python package  to read and parse the VCF file To be readable and parsable by cyvcf2 the VCf file has to be compressed and indexed with one of the 2 following command lines:
bgzip input_vcf_file.vcf tabix -p input_vcf_file.vcf.gz
bcftools view input_vcf_file.vcf -Oz -o input_vcf_file.vcf.gz bcftools index input_vcf_file.vcf.gz
Pop-Con has been developped on VCF files produced with GATK  and read2snp  variant callers. Variant caller used to produced VCF file has to be given with option
--tool (GATK is the default variant caller).
--marft filtering options can be used to test different set of genotype filtering:
--readoption take as input a list of Minimum Read Coverage threshold (MRCt). Genotype with read coverage lower than threshold will be tagged lowCov
--marftoption take as input a list of Minor Allele Read Frequency threshold (MARFt). Genotype with minor allele read frequency lower than threshold will be tagged lowMARF
For each filtering combination (MRCt + MARFt), Pop-Con plots 2 figures (for SNP and indel):
- with sites where all individuals are genotyped and passed MRCt and MARFt filtering.
- with all sites where at least 1 individual is genotyped and passed MRCt and MARFt filtering.
For figure 1, two plots are produced:
- an upper plot representing the observed proportion of the X most represented genotype profiles for each SFS peak (X is set with the
- a lower plot representing for each peak the expected proportion of genotype profile under the Hardy-Weinberg equilibrium (HWE). Genotype profiles are colored in red if observed genotype profile is Y times upper Hardy-Weinberg expectation, blue if Y times lower and white if at equilibrum (between Y times upper and Y times lower). Where Y is set with the option
For figure 2, only SFS plot with observed genotype profiles proportion is produced. This plot can be used to detect abnormal porpotion of low read coverage, low minor allele read frequency or ungenotyped individuals but display is not satisfying for now...
Pop-Con is supported on Linux with python2 (version==2.7) and python3 (versions>=3.4) and surely supported on Macintosh and Windows with the pypi python packages manager but not tested.
Source from GitHub
This assumes that you have the python modules cyvcf2, numpy and matplotlib installed (cf requirements.txt).
git clone https://github.com/YoannAnselmetti/Pop-Con.git cd Pop-Con python ./Pop-Con
Using pip (recommended)
sudo pip install Pop-Con
In the Pop-Con folder where "setup.py" is located, run:
sudo python setup.py install
If you encountered problem during the installation of cyvcf2 or get this following error message when executing Pop-Con:
Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/local/lib/python3.6/site-packages/cyvcf2/__init__.py", line 1, in <module> from .cyvcf2 import (VCF, Variant, Writer, r_ as r_unphased, par_relatedness, ImportError: /usr/local/lib/python3.6/site-packages/cyvcf2/cyvcf2.cpython-36m-x86_64-linux-gnu.so: undefined symbol: EVP_sha1
You have to install it manually from the source: https://github.com/brentp/cyvcf2
usage: Pop-Con [-h] -i VCF_FILE [-t VARIANT_CALLER] [-r MRCT [MRCT ...]] [-m MARFT [MARFT ...]] [-f VARIANT_CALLER_FILTERING] [-fmono MONOMORPH_FILTERING] [-p PREFIX] [-v VERBOSE] [-o OUTPUT_DIR] [-hf WRITE_HETEROZYGOSITY_FILE] [-sep SEP] [-max MAX_PROFILES] [-fold HWE_FOLD_CHANGE] Pop-Con - A tool to plot SFS with genotype profiles for detection of unexpected population genotype patterns. optional arguments: -h, --help show this help message and exit -i VCF_FILE, --input_file VCF_FILE Variant Calling Format file containing variant calling data. -t VARIANT_CALLER, --tool VARIANT_CALLER Variant calling tool used to call variant. Values: "read2snp" or "GATK". (Default: "GATK") -r MRCT [MRCT ...], --read MRCT [MRCT ...] List of Minimum Read Coverage threshold (MRCt) filtering for each genotype. Values range: [0,infinity[. (Default: ) -m MARFT [MARFT ...], --marft MARFT [MARFT ...] List of Minor Allele Read Frequency threshold (MARFt) for heterozygous genotypes filtering. Values range: [0.0,0.5]. (Default: [0.0]) -f VARIANT_CALLER_FILTERING, --variant_caller_filtering VARIANT_CALLER_FILTERING Boolean to set if variant caller filtering is considered or not. (if "True", sites with TAG column (in VCF) not empty are filtered out from analysis). (Default: True) -fmono MONOMORPH_FILTERING, --monomorph_filtering MONOMORPH_FILTERING Boolean to filter out monomorph sites. ("True": monomorph sites are filtered out from analysis. Reduce drastically the execution time!!!). (Default: True) -p PREFIX, --prefix PREFIX Experiment name (used as prefix for output files). (Default: "exp1") -v VERBOSE, --verbose VERBOSE Verbose intensity. (Default: 1) -o OUTPUT_DIR, --output OUTPUT_DIR Output directory path. (Default: ./) -hf WRITE_HETEROZYGOSITY_FILE, --heterozygosity_file WRITE_HETEROZYGOSITY_FILE Boolean to set if the heterozygosity files (summarizing VCF file for each combination of MRCt and MARF filtering) have to be written or not. (Default: False) -sep SEP, --separator SEP Separator used in genotype profiles. (Default: ",") -max MAX_PROFILES, --max_profiles MAX_PROFILES Maximum number of genotype profiles displayed in SFS plot. (Default: 10) -fold HWE_FOLD_CHANGE, --hwe_fold_change HWE_FOLD_CHANGE Fold change value to define when an observed genotype profile proportion is in excess/deficit compare to the expected value under Hardy-Weinberg Equilibrium (HWE). (Default: 2.0) Source code and manual: http://github.com/YoannAnselmetti/Pop-Con
Below, the minimal command line to run Pop-Con:
python Pop-Con -i input_vcf_file.vcf.gz
If the VCF file contains SNP and indel variants, Pop-Con will create two directories "SNP/" and "indel/" in current directory.
Below, an example on VCF file present in directory "example/data/Lineus_longissimus/":
python Pop-Con -i example/data/Lineus_longissimus/Lineus_longissimus_read10_par0.vcf.gz -p Lineus_longissimus -o example/results/Lineus_longissimus/ -t read2snp -fmono True -max 20
Below the architecture of the output directory "example/results/Lineus_longissimus/" produced by Pop-Con with command line above:
example/results/Lineus_longissimus/ └── SNP ├── heterozygosity │ └── heterozygosity_allFilter_Lineus_longissimus.tab └── MARFt0.0 ├── heterozygosity │ └── read0 │ ├── genotype_profiles_distrib_read0_Lineus_longissimus_SNP_MARFt0.0.tab │ ├── genotype_profiles_per_altNb_read0_Lineus_longissimus_SNP_MARFt0.0_max20_with_all_positions.tab │ ├── genotype_profiles_per_altNb_read0_Lineus_longissimus_SNP_MARFt0.0_max20_with_positions_with_all_individuals_genotyped.tab │ └── heterozygosity_read0_Lineus_longissimus_SNP_MARFt0.0.tab └── SFS_profiles └── read0 ├── SFSplot_genotypes_profiles_read0_Lineus_longissimus_SNP_MARFt0.0_max20_all_positions.pdf └── SFSplot_genotypes_profiles_read0_Lineus_longissimus_SNP_MARFt0.0_max20.pdf
The 2 SFS plot with genotype profiles produced:
For sites where all individuals are genotyped and passed read coverage + minor allele read frequency filtering
For sites where at least 1 individual is genotyped and passed read coverage + minor allele read frequency filtering
 Danecek, P. et al. The variant call format and VCFtools. Bioinformatics 27, 2156–2158 (2011).  Pedersen, B. S. & Quinlan, A. R. cyvcf2: fast, flexible variant analysis with Python. Bioinformatics 33, 1867–1869 (2017).  McKenna, A. et al. The Genome Analysis Toolkit: A MapReduce framework for analyzing next-generation DNA sequencing data. Genome Res. 20, 1297–1303 (2010).  Gayral, P. et al. Reference-Free Population Genomics from Next-Generation Transcriptome Data and the Vertebrate–Invertebrate Gap. PLOS Genetics 9, e1003457 (2013).
You get the following error message, when you forgot to set the option
Traceback (most recent call last): File "./Pop-Con", line 404, in <module> individuals_number,dict_SNP_genotypes,dict_indel_genotypes=read_VCF_file(vcf_file,prefix,OUTPUT,list_read_coverage_threshold,list_MARFt,monomorph_filtering,sep,verbose) File "./Pop-Con", line 127, in read_VCF_file dict_SNP_genotypes,dict_SNP_SFS_allPos,dict_SNP_SFS_allIndGT,dict_SNP_hetero,dict_FIS=heterozygosity.store_polymorphism(variant,list_Individuals,dict_SNP_genotypes,dict_SNP_SFS_allPos,dict_SNP_SFS_allIndGT,dict_SNP_hetero,dict_FIS,OUTPUT,'SNP',prefix,list_read_coverage_threshold,list_MARFt,False,variant_caller,write_heterozygosity_file,sep,verbose) File "/home/yanselmetti/Bureau/Pop-Con/popcon/heterozygosity.py", line 365, in store_polymorphism variant_size,x,y,z,listInd,dict_SFS_allPos,dict_SFS_allIndGT=store_SFS(variant,dict_SFS_allPos,dict_SFS_allIndGT,read_coverage_threshold,MARFt,bool_INDEL,variant_caller,verbose) File "/home/yanselmetti/Bureau/Pop-Con/popcon/heterozygosity.py", line 212, in store_SFS alt,x,y,z,listInd=get_polymorphism_GATK(variant,read_coverage_threshold,MARFt) File "/home/yanselmetti/Bureau/Pop-Con/popcon/heterozygosity.py", line 54, in get_polymorphism_GATK str_coverage=str(variant).split()[x].split(":") IndexError: list index out of range
This error can also arise if you used an other variant caller tool than GATK or read2snp as Pop-Con was only tested on VCF files produced by those. If you encountered such problem can you please write an issue, I'll try to shortly produce a new module to parse the VCF produced by the variant caller you used.
For R lovers, there is an extra script ("scripts/SFS_genotypes_profiles_plot.R") to plot SFS with genotype profiles from file. Example:
Rscript ./scripts/SFS_genotypes_profiles_plot.R example/results/Lineus_longissimus/SNP/MARFt0.0/heterozygosity/read0/genotype_profiles_per_altNb_read0_Lineus_longissimus_SNP_MARFt0.0_max20_with_positions_with_all_individuals_genotyped.tab 20 6 Lineus_longissimus example/results/Lineus_longissimus/SNP/MARFt0.0/SFS_profiles/read0/SFSplot_genotypes_profiles_read0_Lineus_longissimus_SNP_MARFt0.0_max20_with_Rscript.pdf 0