tn93 1.1.2

A python implementation of the Tamura-Nei pairwise distance calculation

Tamura-Nei Distance Calculation with Python

Overview

This repository contains a Python implementation of the Tamura-Nei (TN93) distance calculation. When provided with two sequences to compare, this software returns a distance value between 0 and 1 using the Tamura-Nei nucleotide substitution model. See Estimation of the number of nucleotide substitutions in the control region of mitochondrial DNA in humans and chimpanzees for more information on the algorithm. This software has been developed by the Molecular Epidemiology and Bioinformatics Team in the Division of HIV/AIDS Prevention, NCHHSTP.

Usage

This tool is primarily meant as a library to be imported and used in custom analysis code, but can also be used to directly calculate the pairwise distances for a set of sequences in a FASTA file.

First, install using pip

pip install tn93

or clone this respository and copy src/tn93/tn93.py to your working directory. To calculate the distance between a pair of sequences,

from Bio import SeqIO
import tn93
# Read in a FASTA file to get sequences
seqs = [ x for x in SeqIo.parse("your_sequences.fasta", format="fasta") ]
tn93 = tn93.TN93()
distance = tn93.tn93_distance(seqs[0], seqs[1], "RESOLVE")

Alternatively, the module can be run from the command line and provided with a sequence file and match mode to produce a JSON file with the pairwise distances.

python tn93.py --input_file example_seqs.fasta --match_mode RESOLVE --output example_seqs_resolve_distance.json

By default, the software produces distances in the form

ID1,ID2,Distance

Selecting JSON output produces distances in the form

{"ID1": ID1, "ID2": ID2, "Distance": Distance}

There are four distinct match modes:

• SKIP, which ignores ambiguous positions
• GAPMM, which treats gaps appearing in only one sequence as mismatches
• AVERAGE, which takes the average of the possible resolution values
• RESOLVE, which tries to resolve the ambiguity to a single nucleotide, averages if that fails

usage: tn93.py [-h] -i INPUT_FILE -m MATCH_MODE -o OUTPUT
               [-g MAX_AMBIG_FRACTION] [-v] [-n] [-j]

optional arguments:
  -h, --help            show this help message and exit
  -i INPUT_FILE, --input_file INPUT_FILE
                        Path to the input fasta file
  -m MATCH_MODE, --match_mode MATCH_MODE
                        How to handle ambiguities. This can be one of four
                        options: average - Averages the possible nucleotide
                        values for each ambiguity in a sequence; resolve -
                        Tries to resolve ambiguities; skip - Ignores gaps and
                        ambiguities; gapmm - Treats gaps in only one sequence
                        as 'N's;
  -o OUTPUT, --output OUTPUT
                        The name of the output file to create
  -g MAX_AMBIG_FRACTION, --max_ambig_fraction MAX_AMBIG_FRACTION
                        Sequences that have proportions of ambiguities lower
                        than this value will be resolved, otherwise they will
                        be averaged (RESOLVE only) (Default: 1.0)
  -v, --verbose         Verbosity, One copy prints intermediate values and
                        final counts, two copies produces a CSV file with
                        pairwise counts for each non-gap nucleotide
  -n, --ignore_terminal_gaps
                        Should gaps at the beginning and end of a sequence be
                        ignored (GAPMM only)? (Default: False)
  -j, --json_output     Should the output be in JSON format? (Default: False)

Related documents

• Open Practices
• Rules of Behavior
• Thanks and Acknowledgements
• Disclaimer
• Contribution Notice
• Code of Conduct

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Additional Standard Notices

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