                                  frestdist



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Function

   Calculate distance matrix from restriction sites or fragments

Description

   Distances calculated from restriction sites data or restriction
   fragments data. The restriction sites option is the one to use to also
   make distances for RAPDs or AFLPs.

Algorithm

   Restdist reads the same restriction sites format as RESTML and computes
   a restriction sites distance. It can also compute a restriction
   fragments distance. The original restriction fragments and restriction
   sites distance methods were introduced by Nei and Li (1979). Their
   original method for restriction fragments is also available in this
   program, although its default methods are my modifications of the
   original Nei and Li methods.

   These two distances assume that the restriction sites are accidental
   byproducts of random change of nucleotide sequences. For my restriction
   sites distance the DNA sequences are assumed to be changing according
   to the Kimura 2-parameter model of DNA change (Kimura, 1980). The user
   can set the transition/transversion rate for the model. For my
   restriction fragments distance there is there is an implicit assumption
   of a Jukes-Cantor (1969) model of change, The user can also set the
   parameter of a correction for unequal rates of evolution between sites
   in the DNA sequences, using a Gamma distribution of rates among sites.
   The Jukes-Cantor model is also implicit in the restriction fragments
   distance of Nei and Li(1979). It does not allow us to correct for a
   Gamma distribution of rates among sites.

  Restriction Sites Distance

   The restriction sites distances use data coded for the presence of
   absence of individual restriction sites (usually as + and - or 0 and
   1). My distance is based on the proportion, out of all sites observed
   in one species or the other, which are present in both species. This is
   done to correct for the ascertainment of sites, for the fact that we
   are not aware of many sites because they do not appear in any species.

   My distance starts by computing from the particular pair of species the
   fraction

                 n++
   f =  ---------------------
         n++ + 1/2 (n+- + n-+)


   where n++ is the number of sites contained in both species, n+- is the
   number of sites contained in the first of the two species but not in
   the second, and n-+ is the number of sites contained in the second of
   the two species but not in the first. This is the fraction of sites
   that are present in one species which are present in both. Since the
   number of sites present in the two species will often differ, the
   denominator is the average of the number of sites found in the two
   species.

   If each restriction site is s nucleotides long, the probability that a
   restriction site is present in the other species, given that it is
   present in a species, is

      Qs,

   `where Q is the probability that a nucleotide has no net change as one
   goes from the one species to the other. It may have changed in between;
   we are interested in the probability that that nucleotide site is in
   the same base in both species, irrespective of what has happened in
   between. The distance is then computed by finding the branch length of
   a two-species tree (connecting these two species with a single branch)
   such that Q equals the s-th root of f. For this the program computes Q
   for various values of branch length, iterating them by a Newton-Raphson
   algorithm until the two quantities are equal.

   The resulting distance should be numerically close to the original
   restriction sites distance of Nei and Li (1979) when divergence is
   small. Theirs computes the probability of retention of a site in a way
   that assumes that the site is present in the common ancestor of the two
   species. Ours does not make this assumption. It is inspired by theirs,
   but differs in this detail. Their distance also assumes a Jukes-Cantor
   (1969) model of base change, and does not allow for transitions being
   more frequent than transversions. In this sense mine generalizes theres
   somewhat. Their distance does include, as mine does as well, a
   correction for Gamma distribution of rate of change among nucleotide
   sites.

   I have made their original distance available here

  Restriction Fragments Distance

   For restriction fragments data we use a different distance. If we
   average over all restriction fragment lengths, each at its own expected
   frequency, the probability that the fragment will still be in existence
   after a certain amount of branch length, we must take into account the
   probability that the two restriction sites at the ends of the fragment
   do not mutate, and the probability that no new restriction site occurs
   within the fragment in that amount of branch length. The result for a
   restriction site length of s is:

                Q2s
          f = --------
               2 - Qs


   (The details of the derivation will be given in my forthcoming book
   Inferring Phylogenies (to be published by Sinauer Associates in 2001).
   Given the observed fraction of restriction sites retained, f, we can
   solve a quadratic equation from the above expression for Qs. That makes
   it easy to obtain a value of Q, and the branch length can then be
   estimated by adjusting it so the probability of a base not changing is
   equal to that value. Alternatively, if we use the Nei and Li (1979)
   restriction fragments distance, this involves solving for g in the
   nonlinear equation

       g  =  [ f (3 - 2g) ]1/4

   and then the distance is given by

       d  =  - (2/r) loge(g)

   where r is the length of the restriction site.

   Comparing these two restriction fragments distances in a case where
   their underlying DNA model is the same (which is when the
   transition/transversion ratio of the modified model is set to 0.5), you
   will find that they are very close to each other, differing very little
   at small distances, with the modified distance become smaller than the
   Nei/Li distance at larger distances. It will therefore matter very
   little which one you use.

  A Comment About RAPDs and AFLPs

   Although these distances are designed for restriction sites and
   restriction fragments data, they can be applied to RAPD and AFLP data
   as well. RAPD (Randomly Amplified Polymorphic DNA) and AFLP (Amplified
   Fragment Length Polymorphism) data consist of presence or absence of
   individual bands on a gel. The bands are segments of DNA with PCR
   primers at each end. These primers are defined sequences of known
   length (often about 10 nucleotides each). For AFLPs the reolevant
   length is the primer length, plus three nucleotides. Mutation in these
   sequences makes them no longer be primers, just as in the case of
   restriction sites. Thus a pair of 10-nucleotide primers will behave
   much the same as a 20-nucleotide restriction site, for RAPDs (26 for
   AFLPs). You can use the restriction sites distance as the distance
   between RAPD or AFLP patterns if you set the proper value for the total
   length of the site to the total length of the primers (plus 6 in the
   case of AFLPs). Of course there are many possible sources of noise in
   these data, including confusing fragments of similar length for each
   other and having primers near each other in the genome, and these are
   not taken into account in the statistical model used here.

Usage

   Here is a sample session with frestdist


% frestdist
Calculate distance matrix from restriction sites or fragments
Input file: restdist.dat
Phylip restdist program output file [restdist.frestdist]:


Restriction site or fragment distances, version 3.69.650

Distances calculated for species
    Alpha        ....
    Beta         ...
    Gamma        ..
    Delta        .
    Epsilon

Distances written to file "restdist.frestdist"

Done.



   Go to the input files for this example
   Go to the output files for this example

Command line arguments

Calculate distance matrix from restriction sites or fragments
Version: EMBOSS:6.5.0.0

   Standard (Mandatory) qualifiers:
  [-data]              discretestates File containing one or more sets of
                                  restriction data
  [-outfile]           outfile    [*.frestdist] Phylip restdist program output
                                  file

   Additional (Optional) qualifiers (* if not always prompted):
   -[no]restsites      boolean    [Y] Restriction sites (put N if you want
                                  restriction fragments)
   -neili              boolean    [N] Use original Nei/Li model (default uses
                                  modified Nei/Li model)
*  -gammatype          boolean    [N] Gamma distributed rates among sites
*  -gammacoefficient   float      [1] Coefficient of variation of substitution
                                  rate among sites (Number 0.001 or more)
   -ttratio            float      [2.0] Transition/transversion ratio (Number
                                  0.001 or more)
   -sitelength         integer    [6] Site length (Integer 1 or more)
   -lower              boolean    [N] Lower triangular distance matrix
   -printdata          boolean    [N] Print data at start of run
   -[no]progress       boolean    [Y] Print indications of progress of run

   Advanced (Unprompted) qualifiers: (none)
   Associated qualifiers:

   "-outfile" associated qualifiers
   -odirectory2        string     Output directory

   General qualifiers:
   -auto               boolean    Turn off prompts
   -stdout             boolean    Write first file to standard output
   -filter             boolean    Read first file from standard input, write
                                  first file to standard output
   -options            boolean    Prompt for standard and additional values
   -debug              boolean    Write debug output to program.dbg
   -verbose            boolean    Report some/full command line options
   -help               boolean    Report command line options and exit. More
                                  information on associated and general
                                  qualifiers can be found with -help -verbose
   -warning            boolean    Report warnings
   -error              boolean    Report errors
   -fatal              boolean    Report fatal errors
   -die                boolean    Report dying program messages
   -version            boolean    Report version number and exit


Input file format

   frestdist input is fairly standard, with one addition. As usual the
   first line of the file gives the number of species and the number of
   sites, but there is also a third number, which is the number of
   different restriction enzymes that were used to detect the restriction
   sites. Thus a data set with 10 species and 35 different sites,
   representing digestion with 4 different enzymes, would have the first
   line of the data file look like this:

   10   35    4


   The site data are in standard form. Each species starts with a species
   name whose maximum length is given by the constant "nmlngth" (whose
   value in the program as distributed is 10 characters). The name should,
   as usual, be padded out to that length with blanks if necessary. The
   sites data then follows, one character per site (any blanks will be
   skipped and ignored). Like the DNA and protein sequence data, the
   restriction sites data may be either in the "interleaved" form or the
   "sequential" form. Note that if you are analyzing restriction sites
   data with the programs DOLLOP or MIX or other discrete character
   programs, at the moment those programs do not use the "aligned" or
   "interleaved" data format. Therefore you may want to avoid that format
   when you have restriction sites data that you will want to feed into
   those programs.

   The presence of a site is indicated by a "+" and the absence by a "-".
   I have also allowed the use of "1" and "0" as synonyms for "+" and "-",
   for compatibility with MIX and DOLLOP which do not allow "+" and "-".
   If the presence of the site is unknown (for example, if the DNA
   containing it has been deleted so that one does not know whether it
   would have contained the site) then the state "?" can be used to
   indicate that the state of this site is unknown.

  Input files for usage example

  File: restdist.dat

   5   13   2
Alpha     ++-+-++--+++-
Beta      ++++--+--+++-
Gamma     -+--+-++-+-++
Delta     ++-+----++---
Epsilon   ++++----++---

Output file format

   frestdist output contains on its first line the number of species. The
   distance matrix is then printed in standard form, with each species
   starting on a new line with the species name, followed by the distances
   to the species in order. These continue onto a new line after every
   nine distances. If the L option is used, the matrix or distances is in
   lower triangular form, so that only the distances to the other species
   that precede each species are printed. Otherwise the distance matrix is
   square with zero distances on the diagonal. In general the format of
   the distance matrix is such that it can serve as input to any of the
   distance matrix programs.

   If the option to print out the data is selected, the output file will
   precede the data by more complete information on the input and the menu
   selections. The output file begins by giving the number of species and
   the number of characters.

   The distances printed out are scaled in terms of expected numbers of
   substitutions per DNA site, counting both transitions and transversions
   but not replacements of a base by itself, and scaled so that the
   average rate of change, averaged over all sites analyzed, is set to
   1.0. Thus when the G option is used, the rate of change at one site may
   be higher than at another, but their mean is expected to be 1.

  Output files for usage example

  File: restdist.frestdist

    5
Alpha       0.000000  0.022368  0.107681  0.082639  0.095581
Beta        0.022368  0.000000  0.107681  0.082639  0.056895
Gamma       0.107681  0.107681  0.000000  0.192466  0.207319
Delta       0.082639  0.082639  0.192466  0.000000  0.015945
Epsilon     0.095581  0.056895  0.207319  0.015945  0.000000

Data files

   None

Notes

   None.

References

   None.

Warnings

   None.

Diagnostic Error Messages

   None.

Exit status

   It always exits with status 0.

Known bugs

   None.

See also

                    Program name                         Description
                    distmat      Create a distance matrix from a multiple sequence alignment
                    ednacomp     DNA compatibility algorithm
                    ednadist     Nucleic acid sequence distance matrix program
                    ednainvar    Nucleic acid sequence invariants method
                    ednaml       Phylogenies from nucleic acid maximum likelihood
                    ednamlk      Phylogenies from nucleic acid maximum likelihood with clock
                    ednapars     DNA parsimony algorithm
                    ednapenny    Penny algorithm for DNA
                    eprotdist    Protein distance algorithm
                    eprotpars    Protein parsimony algorithm
                    erestml      Restriction site maximum likelihood method
                    eseqboot     Bootstrapped sequences algorithm
                    fdiscboot    Bootstrapped discrete sites algorithm
                    fdnacomp     DNA compatibility algorithm
                    fdnadist     Nucleic acid sequence distance matrix program
                    fdnainvar    Nucleic acid sequence invariants method
                    fdnaml       Estimate nucleotide phylogeny by maximum likelihood
                    fdnamlk      Estimates nucleotide phylogeny by maximum likelihood
                    fdnamove     Interactive DNA parsimony
                    fdnapars     DNA parsimony algorithm
                    fdnapenny    Penny algorithm for DNA
                    fdolmove     Interactive Dollo or polymorphism parsimony
                    ffreqboot    Bootstrapped genetic frequencies algorithm
                    fproml       Protein phylogeny by maximum likelihood
                    fpromlk      Protein phylogeny by maximum likelihood
                    fprotdist    Protein distance algorithm
                    fprotpars    Protein parsimony algorithm
                    frestboot    Bootstrapped restriction sites algorithm
                    frestml      Restriction site maximum likelihood method
                    fseqboot     Bootstrapped sequences algorithm
                    fseqbootall  Bootstrapped sequences algorithm

Author(s)

                    This program is an EMBOSS conversion of a program written by Joe
                    Felsenstein as part of his PHYLIP package.

                    Please report all bugs to the EMBOSS bug team
                    (emboss-bug (c) emboss.open-bio.org) not to the original author.

History

                    Written (2004) - Joe Felsenstein, University of Washington.

                    Converted (August 2004) to an EMBASSY program by the EMBOSS team.

Target users

                    This program is intended to be used by everyone and everything, from
                    naive users to embedded scripts.

Comments

None
