Molecular Phylogenetic Analyses in Court Trials

Fernando González‐Candelas, University of Valencia, Valencia, Spain

Published online: January 2010

DOI: 10.1002/9780470015902.a0021575

Molecular phylogenetics allows reconstructing of the genealogy and evolutionary history of organisms from information on their nucleotide or amino acid sequences. When sequences are derived from very fast evolving organisms, such as ribonucleic acid (RNA) 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 event is the transmission of one of these viruses, for instance human immunodeficiency virus (HIV) or hepatitis C virus (HCV), from an infected person to another. This occasionally results in a legal demand seeking for compensation and/or punishment for the transmitter. Hence, expert testimony is sought in court to determine whether the viruses isolated from the source and the infected patients 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 split in 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 as well as 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.

Keywords: RNA viruses; forensic analysis; likelihood; phylogenetic trees; hypothesis testing

Figure 1. Testing alternative phylogenetic hypotheses. The tree on the left represents the original reconstruction obtained from clone sequences derived from several control (blue) and outbreak (red) samples of HCV E1–E2 region. Two groups are marked for illustration purposes. In the central figure, sequences from sample A are shifted from the outbreak clade to the control group, thus allowing testing the likelihood of the corresponding change for assigning patient A from the outbreak to the control population. In the right tree, the same procedure is applied to sequences from sample B, originally a control patient, which is now considered as belonging to the outbreak group.
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Article Title: Molecular Phylogenetic Analyses in Court Trials
 
How to Cite close
González‐Candelas, Fernando(Jan 2010) Molecular Phylogenetic Analyses in Court Trials. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021575]