def dna(self, dna):
        """ 
        Replace this chromosome's DNA with new DNA of equal length,
        assigning the new DNA to the chromosome's genes sequentially.
        
        For example, if a chromosome contains these genes...
          1. 100100
          2. 011011
          
          ...and the new DNA is 111111000000, the genes become:
          1. 111111
          2. 000000
        """
        assert self.length == len(dna)
        i = 0
        
        for gene in self.genes:
            gene.dna = dna[i:i + gene.length]
            
            i += gene.length