Forensic DNA Profiling
Contents:
Forensic DNA Testing
Current DNA Profiling
Limitations of STR Analysis
Using SNPs in Forensics
Forensic DNA Testing
DNA technology is increasingly vital to ensuring accuracy and fairness in the criminal justice system. The use of DNA typing in human genome
analysis is increasing and finding widespread application in the area of forensic and paternity testing. When used to its full potential, DNA
evidence will help solve and may even prevent some of the most violent crimes. However, the current federal and state DNA collection and analysis
systems in the United States need improvement. The National Institute of Justice estimates that the current backlog of rape and homicide cases is
approximately 350,000, while the FBI casework analysis unit has a backlog of approximately 900 cases. Research to develop faster methods for
analyzing DNA evidence may eventually help reduce or eliminate such backlogs at the state and federal level.
Current DNA Profiling
Modern DNA profiling techniques rely on short tandem repeat (STR) analysis, a technology used in forensics since 1994. Because the number of
repeats in STR loci varies from person to person, examination multiple regions yields a unique profile for every individual. STR analysis using
10 loci lowers the odds of two people having an identical profile to less than one in a billion. Chance matches are even less likely in the
United States, where the FBI routinely examines 13 STR sites to build a DNA profile.
Limitations of STR Analysis
While STR-based DNA profiles are highly accurate and are available in a combined nationwide database (CODIS), this technique for DNA profiling
has some disadvantages. Because measuring the length of STR regions requires gel electrophoresis,
STR analysis is slow compared to high-throughput DNA analysis technologies.
Profiles generated using STR are also expensive; it currently costs around $100 to profile a single individual.
Using SNPs in Forensics
Single-nucleotide polymorphisms (SNPs) are useful genetic markers for DNA analysis. These single-base loci have already proven useful in
identifying disease genes and predicting a patient's potential reaction to experimental drugs (Science, 17 March, p. 1898). SNPs offer several
advantages that make them ideal for forensic DNA testing. SNP analysis is better suited to highly degraded DNA, since assays can be designed with
very small distances between primer binding sites. Recent advances in SNP analysis techniques and collaborative efforts by groups such as the
International HapMap Project
have yielded vast knowledge and data sets related to SNPs in the human genome; now over thirteen million human SNPs are available in
public databases. Most importantly, the high throughput possibilities for SNP genotyping make them more cost-effective to analyze.
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