Summary

Bio::PopGen::Simulation::GeneticDrift - A simple genetic drift simulation

Package variables

Included modules

Inherit

Bio::Root::Root

Synopsis

  use Bio::PopGen::Simulation::GeneticDrift;
  my $sim = new Bio::PopGen::Simulation::GeneticDrift(-popsize => 40,
						      -alleles => {A => 0.2,
							           B => 0.8});
  for(my $i =0 ;$i < 10; $i++ ) {
    my %f = $sim->next_generation; # get the freqs for each generation
  }

  for(my $i =0 ;$i < 10; $i++ ) {
    # get the allele freqs as part of a Bio::PopGen::Population object
    my $pop = $sim->next_generation('population'); 
  }

Description

A very simple 1 locus multi-allele random drift module, start with an
initial set of allele frequency and simulate what happens over time.
This isn't really useful for anything in particular yet but will be
built upon.
See Gillespie JH. (1998) "Population Genetics: a Concise guide." The Johns
Hopkins University Press, Baltimore, USA. pp.19-47.

Methods

Methods description

 Title   : new
 Usage   : my $obj = new Bio::PopGen::Simulation::GeneticDrift();
 Function: Builds a new Bio::PopGen::Simulation::GeneticDrift object 
 Returns : an instance of Bio::PopGen::Simulation::GeneticDrift
 Args    : -popsize => starting N
           -haploid => boolean if we should simulate haploids 
           -alleles => arrayref of the allele names
           OR
           -population => Bio::PopGen::PopulationI object to initialize 
                          from some previously defined Population object
                          (or result from a previous simulation)

 Title   : next_generation
 Usage   : my %generation = $sim->next_generation
 Function: Get the next generation of allele frequencies based on the current
           generation
 Returns : Hash of allele frequencies
 Args    : 'allelefreqs' or 'population' to get back a hash of allele 
                 frequencies (default) OR a Bio::PopGen::Population object

 Title   : population_size
 Usage   : $obj->population_size($newval)
 Function: 
 Example : 
 Returns : value of population_size (a scalar)
 Args    : on set, new value (a scalar or undef, optional)

 Title   : set_Frequencies_Equivalent
 Usage   : $sim->set_Frequencies_Equivalent
 Function: Reset the allele frequencies so they are all even
 Returns : none
 Args    : none

 Title   : get_Allele_Frequencies
 Usage   : my %allele_freqs = $marker->get_Allele_Frequencies;
 Function: Get the alleles and their frequency (set relative to
           a given population - you may want to create different
           markers with the same name for different populations
           with this current implementation
 Returns : Associative array where keys are the names of the alleles
 Args    : none

 Title   : add_Allele_Frequency
 Usage   : $marker->add_Allele_Frequency($allele,$freq)
 Function: Adds an allele frequency
 Returns : None
 Args    : $allele - allele name
           $freq   - frequency value

 Title   : reset_alleles
 Usage   : $marker->reset_alleles();
 Function: Reset the alleles for a marker
 Returns : None
 Args    : None

 Title   : validate_Frequencies
 Usage   : if( $sim->validate_Frequencies) {}
 Function: Sanity checker that allele frequencies sum to 1 or less
 Returns : boolean
 Args    : -strict => 1 boolean if you want to insure that sum of freqs is 1

Methods code

sub new {

  my($class,@args) = @_;

  my $self = $class->SUPER::new(@args);
  my ($population,
      $popsize, $haploid, $alleles) = $self->_rearrange([qw(POPULATION
							    POPSIZE
							    HAPLOID
							    ALLELES)],@args);
  if( defined $population && ref($population) &&
      $population->isa('Bio::PopGen::PopulationI') ) {
      $self->population_size($population->get_number_individuals || $popsize);
      my %f = $population->get_Allele_Frequencies;
      while( my ($allele,$freq) = each %f ) {
	  $self->add_Allele_Frequency($allele,$freq);
      }
  } else { 
      $self->population_size($popsize);  
  
      if( ! defined $alleles || ref($alleles) !~ /HASH/i  ) {
	  $self->throw("Must provide a valid set of initial allele frequencies to $class as an hashref");
      } 
      while( my ($allele,$freq) = each %$alleles ) {
	  $self->add_Allele_Frequency($allele,$freq);
      }
  }
  unless( $self->validate_Frequencies ) {
      $self->throw("You specified allele frequencies which summed to more than 1");
  }
  return $self;

}

sub next_generation {

   my ($self,$rettype) = @_;
   my %initial = $self->get_Allele_Frequencies;
   my $popsize = $self->population_size || 
       $self->throw("Need to have set a valid population size when running the simulation");
   # we're going to construct a mapping of the rational space from 0->1 
   # which will map to a particular allele and be proportional to it
   # frequency
   my ($last,@mapping) = (0);

   # we'll make ranges that cover from >= left and < right in terms of the
   # order doesn't matter - 'distance' does
   # range that we're going to try and match
   # since rand() goes from 0 up to 1 (not including 1)
   foreach my $a ( keys %initial ) {
       push @mapping, [$last,$initial{$a}+$last,$a];
       $last += $initial{$a};
   }

   my %f;
   for( my $i =0; $i < $popsize; $i++ ) {
       my $rand = rand(1);
       foreach my $val ( @mapping ) {
	   if( $rand >= $val->[0] && $rand < $val->[1] ) {
	       $f{$val->[2]}++;
	       last;
	 }
       }
   }
   foreach my $f ( values %f ) {
       $f /= $popsize;
   }
   %{$self->{'_allele_freqs'}} = %f;
   
   if( defined $rettype && 
       $rettype =~ /population/i) {
       return Bio::PopGen::Poulation->new(-frequencies =>\% f);
   } else { 
       return %f;
   }

}

sub population_size {

    my $self = shift;

    return $self->{'_population_size'} = shift if @_;
    return $self->{'_population_size'};

}

sub set_Frequencies_Equivalent {

   my ($self) = @_;
   my @alleles = keys %{$self->{'_allele_freqs'}};
   my $eqfreq  = 1 / scalar @alleles;
   for ( @alleles ) { $self->{'_allele_freqs'}->{$_} = $eqfreq }
   return;

}

sub get_Allele_Frequencies {

   return %{$_[0]->{'_allele_freqs'}};

}

sub add_Allele_Frequency {

   my ($self,$allele,$freq) = @_;
   $self->{'_allele_freqs'}->{$allele} = $freq;

}

sub reset_alleles {

   my ($self) = @_;
   $self->{'_allele_freqs'} = {};

}

sub validate_Frequencies {

   my ($self,@args) = @_;
   my ($strict) = $self->_rearrange([qw(STRICT)], @args);
   my $sum = 0;
   my %freq = $self->get_Allele_Frequencies;
   foreach my $f ( values %freq ) { 
       $sum += $f;
   }
   return ($strict) ? $sum == 1 : $sum <= 1;

}

General documentation

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The rest of the documentation details each of the object methods.
Internal methods are usually preceded with a _