MITOCHONDRIAL PORTRAITS OF HUMAN-POPULATIONS USING MEDIAN NETWORKS

Analysis of variation in the hypervariable region of mitochondrial DNA (mtDNA) has emerged as an important tool for studying human evolution and migration. However, attempts to reconstruct optimal intraspecific mtDNA phylogenies frequently fail because parallel mutation events pa rtly obscure the true evolutionary pathways. This makes it inadvisable to present a single phylogenetic tree at the expense of neglecting eq ually acceptable ones. As an alternative, we propose a novel network a pproach for portraying mtDNA relationships. For small sample sizes (< similar to 50), an unmodified median network contains all most parsimo nious trees, displays graphically the full information content of the sequence data, and can easily be generated by hand. For larger sample sizes, we reduce the complexity of the network by identifying parallel isms. This reduction procedure is guided by a compatibility argument a nd an addi- tional source of phylogenetic information: the frequencies of the mitochondrial haplotypes. As a spinoff, our approach can also assist in identifying sequencing errors, which manifest themselves in implausible network substructures. We illustrate the advantages of our approach with several examples from existing data sets.