Molecular relationship between 54 SARS-CoV genomes. The phylogenetic tree reconstructed using PAUP* on nucleotide variations shared by more than two isolates. The tree was re-rooted on the earliest reported case, i.e. TOR2. Four major branches can be observed in the tree, each largely belonging to a certain geographical origin. Two of which encompass the Singapore cases, indicating the possibility of separate infection sources of the Singapore cases.