Additional Thoughts On Snps

SNP typing is already in production use for human identity applications. A modified version of Genetic Bit Analysis (Nikiforov et al. 1994), called SNP-IT that runs on the SNPstream UHT platform (Bell et al. 2002), has been used by Orchid Cellmark (Dallas, TX) to genotype multiple SNP markers for paternity applications and examine highly degraded samples from mass disasters (see Chapter 24). The forensic DNA typing community will likely hear more about these SNP markers and assays in the future.

As the Human Genome Project and now the International HapMap effort, along with various commercial ventures, continue to improve SNP analysis the testing of multiple SNP sites will become less expensive and easier to perform. In the future, SNP detection platforms may be used in conjunction with fluorescent STR results to establish DNA profiles of forensic casework samples. Some technologies, such as capillary array electrophoresis, mass spectrometry and microchip array hybridization using electronic stringency (see Chapter 17), are capable of performing analysis on both STR and SNP markers.

For SNPs to become more widely used in the future of forensic DNA testing, it is important that the field settle on common loci. STR typing was propelled forward when the Second Generation Multiplex was introduced and used to launch the United Kingdom's National DNA Database (see Chapter 18). Likewise, the selection of 13 core loci for the Combined DNA Index System (CODIS) aided standardization of information in the United States and around the world (see Chapter 5). To aid in cataloging SNP loci of forensic interest and collating features of the markers in a common format, the U.S. National Institute of Standards and Technology has set up a forensic SNP web site: http://www.cstl.nist.gov/biotech/strbase/SNP.htm (Gill et al. 2004). This web site is intended to provide a resource to the community as further markers, assays, and technologies are developed for SNP analysis. With gathering this information many loci can be compared and examined for their forensic value to aid in the selection of a consistent set of SNP loci for the community to use as their standard (see Phillips et al. 2004).

It is important to keep in mind that SNPs will not replace STRs in the near or even medium term future as the primary source of information used in criminal investigations. The legacy data from national DNA databases means that STRs are here to stay. Replacing the millions of profiles that exist in large national DNA databases through re-typing convicted offender and casework samples with new SNP markers is neither financially practical nor prudent at this juncture.

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