   2 1  Example: chromosome 1 with single dna segment
9
6    North
n_ind0_a  ccccccAcc
n_ind0_b  TcccccAcc
n_ind1_a  ccccccTcc
n_ind1_b  TcccccTcc
n_ind2_a  ccccccGcc
n_ind2_b  TcccccGcc
4    South
s_ind0_a  cTccTcccc
s_ind0_b  ccccTcccc
s_ind1_a  cTccccccc
s_ind1_b  ccccccccc
