Other DNA Issues

Harry R Erwin, PhDCIS308

Faculty of Applied SciencesUniversity of Sunderland

Topics

• Introduction• DNA structure and the genome• DNA handling procedures• PCR• The use of short tandem repeat data• DNA statistics and evidence• DNA databases• Other markers

References

• Goodwin, Linacre, and Hadi (2007) An Introduction to Forensic Genetics, Wiley.

• Butler (2005) Forensic DNA Typing, 2nd edition, Elsevier.

Lecture Plan

• Presentation of evidence• DNA databases• Other markers• Discussion: DNA evidence in the courtroom

Evaluation and Presentation of Evidence

• Three questions to consider:1. From which individual did the biological material

originate?2. What activity led to the deposition of the

biological material?3. Did the suspect commit the offence?

From which individual did the biological material originate?

• Can be addressed by DNA analysis.• Three approaches:

1. Frequentist approach—random match probability = 1/(profile frequency), with a ceiling in the UK of 1 in a billion. Vulnerable to the base rate fallacy.

2. Likelihood approach—compare two hypotheses, producing a likelihood ratio or a verbal scale.

3. Bayesian approach—not accepted in the UK legal system despite being the most valid.

Warning

• Be precise!• Do not commit the prosecutor’s or the

defendant’s fallacy!

What activity led to the deposition of the biological material?

• Can often be addressed to some extent by the forensic scientist.

Did the suspect commit the offence?

• Provenance of the court.

UK National DNA Database (NDNAD)

• 4,200,000 individuals including many not convicted of any crime.• Justification:

– Criminals tend to reoffend– Severity of crimes tends to increase– A small number of criminals can be responsible for a large number of

crimes• There have been proposals to enter everyone into the NDNAD.• A recent decision by the European Court of Human Rights found

that the police's actions in keeping fingerprints and DNA data from two men never convicted of an offence were in violation of Article 8 - the right to respect for private and family life.

• The UK police and Home Office are stonewalling the decision.

Other Databases

• NZ, Australia, and South Africa on the British model.

• Limited DNA databases in almost all continental EU states.

• Universal databases under development in Kuwait and the UAE.

• CODIS (USA) with crime scene data and profiles of violent criminals. About the same size as the UK database with ten times the population.

Other markers

• Kinship testing– STR profiling, including markers on X and Y

chromosomes– Interpretation is complex, especially within kinship

groups.• Identification of human remains• Lineage markers– mtDNA in women– Y-chromosome STR markers in men

Discussion: DNA evidence in the courtroom

Exploration of DNA Data and Analysis

DNA Data and Documentary Evidence