Molecular Phylogenetic Analyses in Court Trials

Abstract

Molecular phylogenetics allows the reconstruction of the genealogy and evolutionary history of organisms from information in their nucleotide or amino acid sequences. When sequences are derived from very fast‐evolving organisms, such as ribonucleic acid viruses, changes accumulate in a few days or weeks, thus allowing the reconstruction of very recent evolutionary events in the history of these populations. One such is event is the transmission of one of these viruses, for instance human immunodeficiency virus or hepatitis C virus, from an infected person to another or the infection of a person from a contaminated device or material. This occasionally results in a legal demand seeking for compensation and/or punishment for the transmitter. Hence, expert testimony is sought in court in order to determine whether the viruses isolated from the source and the infected patient(s) actually share a common origin or not. Molecular phylogenetics and statistical inference methods are used to translate scientific testimony into expert evaluation of the evidence for the court. Key Concepts Fast‐evolving organisms, such as RNA viruses, can accumulate changes in their genome sequence in a few days or weeks. Changes in nucleotide sequences can be used to track the evolutionary history of organisms sharing a common ancestor. The last common ancestor (LCA) of a set of sequences represents the last sequence before the corresponding lineage splits into two or more separate lines of descent. During a transmission event, a portion of the microorganisms in the source is passed onto the recipient(s). Phylogenetic analysis can be used to ascertain when two or more sequences shared an LCA and some of its features. Sequences derived from a transmission event will share a more recent LCA than those obtained from unrelated sources. The analysis of LCA can be used to provide expert testimony in courts on the source of an infection. Under special conditions, it is also possible to ascertain the direction of the transmission and an approximate time for it. Phylogenetic analysis is a very powerful and reliable methodology whose use for resolving transmission cases has been validated by courts in many countries.