This is just a nifty little script I wrote that will solve a Punnett square. I plan to make it into a full-featured gem that will be used a future project.

punnet_square.rb

module Geneticist
  # The syntax is easy here. If you know how to set up a Punnett Square in real life,
  # it's pretty self explanatory.
  #
  #   # Checking for green eyes
  #   square = Geneticist::PunnettSquare.new('Gg', 'gg')
  #   square.result
  #   #=> {"Gg"=>2, "gg"=>2}
  #
  #   # Checking a cross between a spider ball python and a pastel ball python
  #   square = Geneticist::PunnettSquare.new('Sspp', 'ssPp')
  #   square.result
  #   #=> {"PpSs"=>4, "ppSs"=>4, "Ppss"=>4, "ppss"=>4}
  class PunnettSquare
    attr_accessor :male, :female
    attr_reader :offspring, :result

    def initialize(male, female)
      @male, @female = punnett_permute(male), punnett_permute(female)
      @result = cross
    end

    private

      def cross
        @offspring = @male.map do |top_trait|
          @female.map do |left_trait|
            punnett_sort(top_trait + left_trait)
          end
        end.flatten

        @offspring.inject(Hash.new(0)) { |h,v| h[v] += 1; h }
      end

      # Sorts string to the Punnett square standard
      #
      #   punnett_sort('bBAAcC') # => 'AABbCc'
      #
      def punnett_sort(string)
        string.split('').sort { |x, y| x.downcase <=> y.downcase }.each_slice(2).map { |a| a.sort.join }.join
      end

      # Rearranges arr to form the headers of a Punnett square
      #
      #   punnett_permute('AaBb') # => ['AB', 'Ab', 'aB', 'ab']  
      #
      def punnett_permute(arr)
        arr = arr.split('') if arr.kind_of? String

        # I'm not even entirely sure how this works.
        arr.permutation(arr.length/2).to_a.map(&:join).select do |permutation|
          permutation.split('').each_with_index.select do |e, i| 
            # I mean what the hell is this I don't even
            e.downcase == arr[((i+1)*2)-1].downcase
          end.count == permutation.length
        end
      end
  end
end