Circos > Documentation > Tutorials > Ideograms > Karyotypes
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2 — Drawing Ideograms

2. Karyotypes

The karyotype file defines the axes. In biological context, these are typically chromosomes, sequence contigs or clones.

Each axis (e.g. chromosome) is defined by unique identifier (referenced in data files), label (text tag for the ideogram seen in the image), size and color.

In addition to chromosomes, the karyotype file is used to define position, identity and color of cytogenetic bands. For some genomes these band data are available.

designing the Circos image

The most difficult part of creating a Circos image—any visualization for that matter—is deciding what data to show. Chances are your data is too complex to show (e.g. its native format doesn't have a trivial visual encoding, such as a scatter plot).

Mapping data onto a Circos figure requires that you identify what patterns in your data are (a) likely to be important and (b) likely to be present, and create a figure that exposes such patterns. Remember, if the pattern exists, you can't afford to miss it. If it doesn't exist, you can't afford to be fooled into thinking that it's there, or left wondering whether it's occluded by other data.

If you don't know where to start when creating Circos images from genomic and non-genomic data, look through published examples from the literature. Find images whose patterns map onto your data types.

Don't think necessarily from the point of view of how to construct input files. First, identify what you want to show and how. Make a sketch of the kind of figure you want to make. This is the hard part.

defining chromosomes

Chromosome definitions are formatted as follows


The first two fields are always "chr", indicating that the line defines a chromosome, and "-". The second field defines the parent structure and is used only for band definitions.

The id is the identifier used in data files whereas the LABEL is the text that will appear next to the ideogram on the image. If you are working with multiple species, I suggest prefixing the chromosome number with a species identifier (e.g., hs = Homo sapiens, mm = Mus musculus, etc). Even when working with only one species, prefixing the chromosome with a species code is highly recommended — this will greatly help in creating more transparent configuration and data files.

The start and end values define the size of the chromosome. The karyotype file should store the entire chromsome size, not just the region you wish to draw. Other configuration file parameters control the drawable regions.

The color of the ideogram will be used, if you decide not to show the cytogenetic bands and select the fill option. The color can be useful to distinguish between species and chromosomes. Consider using the conventional chromosome color scheme as defined in the etc/color.conf configuration file. Colors are defined for each human chromosome and are named similiarly: chr1, chr2, ... chrx, chry, chrun. Colors must be in lowercase.

The karyotype file is specified in the configuration file using

karyotype = data/karyotype/karyotype.human.txt

For example, the human karyotype for assembly GRCh37 (hg19, Feb 2009) is composed of 24 chromosomes

chr - hs1 1 0 249250621 chr1
chr - hs2 2 0 243199373 chr2
chr - hs3 3 0 198022430 chr3
chr - hs22 22 0 51304566 chr22
chr - hsX x 0 155270560 chrx
chr - hsY y 0 59373566 chry

together with 862 bands

band hs1 p36.33 p36.33 0 2300000 gneg
band hs1 p36.32 p36.32 2300000 5400000 gpos25
band hs1 p36.31 p36.31 5400000 7200000 gneg
band hsY q11.223 q11.223 22100000 26200000 gpos50
band hsY q11.23 q11.23 26200000 28800000 gneg
band hsY q12 q12 28800000 59373566 gvar

cytogenetic bands

Bands are defined in the same manner as chromosomes, but the first two fields are now band and the id of the parent chromosome.

band hs1 p36.33 p36.33 0 2300000 gneg
band hs1 p36.32 p36.32 2300000 5300000 gpos25
band hs1 p36.31 p36.31 5300000 7100000 gneg
band hs2 p25.3 p25.3 0 4300000 gneg
band hs2 p25.2 p25.2 4300000 7000000 gpos50
band hs2 p25.1 p25.1 7000000 12800000 gneg

You can obtain the karyotype structure from UCSC Genome Viewer Table Browser (Mapping and Sequencing Tracks > Chromosome Band) . Not all genomes have these data, however. For example, mouse (mm9) and rat (rn4) have band information, but not dog (canfam2) or cow (bostau3)

band transparency

Cytogenetic band structure is drawn on top of the ideograms. The ideogram itself can have an associated color—this is defined in the karotype file—and when band transparency is turned on, this color shows through.

show_bands = yes
fill_bands = yes
band_transparency = 4

The value for band_transparency can be 1..auto_alpha_steps, where auto_alpha_steps is the number of automatically generated transparency steps for each color (see etc/image.conf).

When band_transparency=1, the bands are least transparent. Conversely, when band_transparency=auto_alpha_steps, the bands are most transparent. For a given band_transparency value, the opacity is given by band_transparency/(auto_alpha_steps+1) (e.g. 2/6 when band_transparency=2 and auto_alpha_steps=5).

when to use bands

The cytogenetic bands feature is meant ... for cytogenetic bands. These ideogram annotations have two specific properties: they cover the entire ideogram and they don't overlap.

If you want to use the band feature to show other ideogram annotations, the data must meet these two conditions. It's likely that unless your data are cytogenetic banding patterns, they won't (e.g. gene regions, repeat regions, etc). In these case, use the highlight plot block and draw the highlights within the ideograms by setting

r0 = dims(ideogram,radius_inner)
r1 = dims(ideogram,radius_outer)

defining multiple species

If you would like to draw ideograms from multiple species, list their karyotype files in the karyotype parameter

karyotype = data/karyotype/karyotype.human.txt,data/karyotype/karyotype.rat.txt
# data/karyotype/karyotype.human.txt
chr - hs1 1 0 249250621 chr1
chr - hs2 2 0 243199373 chr2
chr - hs3 3 0 198022430 chr3

# data/karyotype/karyotype.rat.txt
chr - rn1 1 0 267910886 chr1
chr - rn2 2 0 258207540 chr2
chr - rn3 3 0 171063335 chr3

non-genomic karyotype files

Circos was designed to draw genomic data, but this isn't a limitation. If you have any positional data that would benefit from a circular composition, you can define abstract "chromosomes" to act as data domains.

For example, consider this "Naming Names" NYT graphic of a presidential debate. This image could be generated with Circos. In this case, the karyotype would define each candidate as a "chromosome", and a segment of speech as a "band". The NYT illustration is a wonderful analogy to comparative genomics - each candidate (a genome) makes verbal reference to (shows synteny) to another candidate (another genome).

If you have two integer ranges 0-1000 over which you wanted to display data, you might define

chr - axis1 1 0 1000 green
chr - axis2 2 0 1000 red

Furthermore, you could use the band functionality to display a checkered grid within each domain to indicate length.

band axis1 band1 band1 0 99 grey
band axis1 band2 band2 100 199 white
band axis1 band1 band1 200 299 grey
band axis1 band2 band2 300 399 white

The definitions in the karyotype file need not correspond to physical structures. Among other things, you can use them to define contigs, such as sequence or map contigs.