Advanced Concepts

Alec Jeffreys' DNA profiling was the basis for the National DNA Database (NDNAD) launched in Britain in 1995. Under British law, the DNA profile of anyone convicted of a serious crime is stored on a database. The database now has DNA information on more than 250,000 people.

Created by the DNA Identification Act of 1994, the National DNA Index System (NDIS) is the federal level of the Combined DNA Indexing System (CODIS) used in the United States. There are three levels of CODIS: the Local DNA Index System (LDIS), State DNA Index System (SDIS), and NDIS. At the local level, CODIS software maintained by the Federal Bureau of Investigation (FBI) is used at the bench in sizing alleles. This information may be applied locally and/or submitted to the SDIS. At the state level, interlaboratory searching occurs. The state data may be sent to the NDIS. The SDIS and NDIS must adhere to the quality assurance standards recommended by the FBI. The original entries to these databases were RFLP profiles; all future entries will be STR profiles. As of 2005, there were 108,976 forensic DNA profiles and 2,390,740 convicted offender profiles in NDIS.

considered different if at least one locus genotype differs (exclusion). An exception is paternity testing, in which mutational events may generate a new allele in the offspring, and this difference may not rule out paternity.

Matching requires clear and unambiguous laboratory results. As alleles are identified by gel resolution, good intragel precision (comparing bands or peaks on the same gel or capillary) and intergel precision (comparing bands or peaks of separate gels or capillaries) are important. In general, intergel precision is less stringent than intragel precision. This is not unexpected because the same samples may run with slightly different migration speeds on different gels. Some microvariant alleles differ by only a single base pair (see Fig. 11-13), so precision must be less than ±0.5 bp. Larger alleles, however, may show larger variation. The TH01 9.3 allele described above is an example. This allele must be distinguished from the 10 allele, which is a single base pair larger than the 9.3 allele.

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