if ( $gene_to < $gene_from ) {

                                        # split
                                        # low range first
                                        $temp_gene_to_legal_range = [
                                        #       { FROM => 0, TO => $gene_to },
                                        #       {
                                        #               FROM => $gene_from,
                                        #               TO   => $zone_o->{_chromosome_length}
                                        #       }
                                          0, $gene_to, $gene_from, $zone_o->{_chromosome_length}
                                        ];
                                }
                                else {

                                        # single
                                        $temp_gene_to_legal_range =
                                        #  [ { FROM => $gene_from, TO => $gene_to } ];
                                          [ $gene_from, $gene_to ]
                                }