Pairwise identity

Pairwise sequence identity in an alignment

Command identity

Canonical command:

pairwise_identity

Handler:

pairwise_identity

Aliases:

pairwise_id, pi

Standalone executables:

pk_pairwise_identity, pk_pairwise_id, pk_pi

Categories:

Alignment quality & statistics

Runtime interface

Synopsis

phykit pairwise_identity <alignment> [--verbose] [--exclude_gaps] [--plot] [--plot-output <plot_output>] [--fig-width <fig_width>] [--fig-height <fig_height>] [--dpi <dpi>] [--no-title] [--title <title>] [--legend-position <legend_position>] [--ylabel-fontsize <ylabel_fontsize>] [--xlabel-fontsize <xlabel_fontsize>] [--title-fontsize <title_fontsize>] [--axis-fontsize <axis_fontsize>] [--colors <colors>] [--ladderize] [--cladogram] [--circular] [--color-file <color_file>] [--json]

Arguments

This table is generated from the live command parser. It is the authoritative source for accepted spellings, required arguments, types, defaults, and choices.

Argument	Required	Type	Default	Choices
alignment	true	str	required	any
-v, --verbose	false	boolean	false	any
-e, --exclude_gaps	false	boolean	false	any
--plot	false	boolean	false	any
--plot-output	false	str	pairwise_identity_heatmap.png	any
--fig-width	false	float	none	any
--fig-height	false	float	none	any
--dpi	false	int	300	any
--no-title	false	boolean	false	any
--title	false	str	none	any
--legend-position	false	str	none	any
--ylabel-fontsize	false	float	none	any
--xlabel-fontsize	false	float	none	any
--title-fontsize	false	float	none	any
--axis-fontsize	false	float	none	any
--colors	false	str	none	any
--ladderize	false	boolean	false	any
--cladogram	false	boolean	false	any
--circular	false	boolean	false	any
--color-file	false	str	none	any
--json	false	boolean	false	any

Output and errors

--json provides the command's structured JSON representation. Output-file options: --plot-output. Invalid command syntax exits with status 2. Input validation and scientific limitations are described in the guidance below.

Guidance, interpretation, and examples

Calculate the average pairwise identity among sequences.

Pairwise identities can be used as proxies for the evolutionary rate of sequences.

Pairwise identity is defined as the number of identical columns (including gaps) between two aligned sequences divided by the number of columns in the alignment. Summary statistics are reported unless used with the verbose option in which all pairwise identities will be reported.

An example of pairwise identities being used as a proxy for evolutionary rate can be found here: Chen et al. Genome Biology and Evolution (2017), doi: 10.1093/gbe/evx147.

phykit pairwise_identity <alignment> [-v/--verbose] [-e/--exclude_gaps] [--plot] [--plot-output <file>]
        [--fig-width <float>] [--fig-height <float>] [--dpi <int>] [--no-title] [--title <str>]
        [--legend-position <str>] [--ylabel-fontsize <float>] [--xlabel-fontsize <float>]
        [--title-fontsize <float>] [--axis-fontsize <float>] [--colors <str>] [--ladderize] [--cladogram] [--circular] [--color-file <file>] [--json]

Options:
<alignment>: first argument after function name should be an alignment file
-v/--verbose: optional argument to print identity per pair
-e/--exclude_gaps: if a site has a gap, ignore it
--plot: save a clustered pairwise-identity heatmap
--plot-output: output path for heatmap (default: pairwise_identity_heatmap.png)
--fig-width: figure width in inches (auto-scaled if omitted)
--fig-height: figure height in inches (auto-scaled if omitted)
--dpi: resolution in DPI (default: 300)
--no-title: hide the plot title
--title: custom title text
--legend-position: legend location (e.g., "upper right", "none" to hide)
--ylabel-fontsize: font size for y-axis labels; 0 to hide
--xlabel-fontsize: font size for x-axis labels; 0 to hide
--title-fontsize: font size for the title
--axis-fontsize: font size for axis labels
--colors: comma-separated colors (hex or named)
--ladderize: ladderize (sort) the tree before plotting
--cladogram: draw cladogram (equal branch lengths, tips aligned) instead of phylogram
--circular: draw circular (radial/fan) phylogram instead of rectangular
--color-file: color annotation file for tip labels, clade ranges, and branch colors (iTOL-inspired TSV format)
--json: optional argument to print results as JSON