NOTE

These scripts can be instructive for understanding how genome size is estimated from k-mer data. If you are looking for a more automated method for estimating genome size check out: http://qb.cshl.edu/genomescope/

NOTE

If after generating a plot, your plot has multiple peaks or no clear peaks, you likely have data with high heterozygosity and/or high duplication. I have not looked further into interpreting the various characteristics of these plots, but if I were to find the time, i would:

1. simulate heterozygosity: artificially add lots of heterozygosity to 2 or 3 copies of HumanChromosome22, then use the ART Illumina-sequence simulator to generate reads, and rerun the estimate_genome_size.pl script. (perhaps run multiple times with increasing levels of "heterozygosity")

2. simulate gene duplication take random chunks of HumanChromosome22 (totaling about 10% of the genome) and generate lots of reads on these chunks using the ART Illumina-sequence simulator, and rerun the estimate_genome_size.pl script. (perhaps run again with 20% or doubling the amount of reads generated on the duplicates).

If you get patterns that look like your scatterplot, it is a decent indication of what is going on with your data. If you do this and would like to share your findings, I would be happy to point to your github repo or post your data/results in a folder on this repo.

NOTE

VERSIONS 0.03 and below do not handle compressed files correctly and therefore give erroneous size estimations. If you used uncompressed files, there is no problem. this has been fixed in VERSION 0.04. -- November 12, 2014

estimate_genome_size.pl

this is a suite of perl scripts to help estimate genome size from KMER distributions. It has been tested with the JELLYFISH program http://www.cbcb.umd.edu/software/jellyfish/

The output looks something like:

Estimated Coverage: 59.5 (60X) Estimated Genome Size: 1010144681.14286 (1GB) 

INSTALLATION

To install this script and documentation type the following:

perl Makefile.PL
make
make install

To install without root privelages try:

perl Makefile.PL PREFIX=/home/myuser/scripts
make
make install

RUN

estimate_genome_size.pl [--version] [--help] --kmer=KMERLEN --peak=PEAK --fastq=fastq [--fastq=fastq]

for detailed documenation

perldoc estimate_genome_size.pl
perldoc find_valleys.pl
perldoc jellyplot.pl

DEPENDENCIES

This module requires Perl

You will also want JELLYFISH:

http://www.cbcb.umd.edu/software/jellyfish/

For the jellyplot program you will need gnuplot in your path:

http://www.gnuplot.info/

A TYPICAL SESSION

# count k-mers (see jellyfish documentation for options)
gzip -dc reads1.fastq.gz reads2.fastq.gz | jellyfish count -m 31 -o fastq.counts -C -s 10000000000 -U 500 -t 30 /dev/fd/0 

# generate a histogram
jellyfish histo fastq.counts_0 > fastq.counts_0.histo

# generate a pdf graph of the histogram
jellyplot.pl fastq.counts_0.histo

# look at fastq.counts_0.histo.pdf and identify the approximate peak

# use find_valleys.pl to help pinpoint the actual peak
find_valleys.pl fastq.counts_0.histo

# estimate the size and coverage
estimate_genome_size.pl --kmer=31 --peak=42 --fastq=reads1.fastq.gz reads2.fastq.gz

SEE THE FOLLOWING FOR THE PRINCIPLE BEHIND THE SCRIPT

https://banana-slug.soe.ucsc.edu/bioinformatic_tools:jellyfish http://seqanswers.com/forums/archive/index.php/t-10988.html https://banana-slug.soe.ucsc.edu/bioinformatic_tools:quake

IF YOU DON'T BELIEVE IT WORKS

Simulate some next generation data based on an already-sequenced genome. I used the program ART to do this with the Hydra magnipapillata genome:

http://www.niehs.nih.gov/research/resources/software/biostatistics/art/

art_illumina --paired --in Hm_genomic.fa --out Hm_genomic_wildtype --len 100 --fcov 43 --mflen 180 --sdev 3.5

I also simulated perfect paired-end data with a sliding window. In both cases I recovered the correct coverage and size.

COPYRIGHT AND LICENSE

Copyright (C) 2012,2013 Joseph F. Ryan

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program in the file gpl.txt. If not, see http://www.gnu.org/licenses/.