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The Combined DNA Index System

Report No. 01-26
September 17, 2001
Office of the Inspector General



CODIS Administrator: the person at each laboratory that is responsible for the administration and security of the laboratory's CODIS program. The position can also be referred to as CODIS Manager or CODIS Custodian. The CODIS Administrator is required by the QAS for each laboratory with a convicted offender database, although all CODIS laboratories should have someone filling that role.

Convicted Offender Database: consists of DNA profiles from convicted offenders. Convicted offenders are persons who have been convicted of crimes in state, and/or local courts where the applicable law permits establishment of a DNA profile for the convicted person.

Deoxyribonucleic Acid (DNA): DNA is found in almost all living cells, and carries the encoded information necessary for building and maintaining life. This encoded information is what makes each person an individual. Human DNA resembles a spiral staircase. The steps of the staircase consist of two of four possible chemicals. The order in which the chemicals are arranged is called the DNA sequence. It is this unique sequence that is determined when a DNA sample is typed.

DNA Profile: a set of DNA identification characteristics, i.e., the particular chemicals at the various DNA locations (loci), which permit the DNA of one person to be distinguishable from that of another person.

DNA Sample: a body tissue or fluid sample (blood or semen for example) that can be subjected to DNA analysis.

DNA Typing: the process by which a DNA sample is examined and a DNA profile is produced.

Forensic Database: consists of DNA profiles from persons whose identities are not known with certainty and who left DNA at the scene of a crime or whose DNA was carried away from it. For example, a DNA profile may be developed from a bloody knife found at a crime scene or found in a trash dumpster.

Investigations Aided: the primary measuring unit that the FBI uses to quantify the success of CODIS. An investigation is aided when a DNA match through CODIS either identifies a potential suspect or links violent crimes together. In addition, the information provided by the DNA match must be new information that would not have been otherwise developed.

Local DNA Index System (LDIS): generally contains DNA profiles for one laboratory. LDIS records are used to search for DNA matches and, at the discretion of the LDIS laboratory, are uploaded to the next CODIS database level (SDIS).

Loci: the plural form of locus.

Locus: a specific physical location on a chromosome. Analogous to an address for a house.

National DNA Index System (NDIS): the FBI-maintained national component to CODIS. NDIS contains DNA profiles uploaded from approved State DNA Index Systems.

Polymerase Chain Reaction (PCR): a method used to replicate specific portions of the DNA strands. The DNA is heated, causing the two strands to separate like a zipper. The two DNA halves are then cooled and mixed with a special enzyme. The result of this process is the creation of two DNA strands identical to each other and to the original DNA strand. This process is repeated many times to replicate a desired DNA sequence millions of times in a matter of hours. PCR is especially valuable because it does not require high quality or large quantities of DNA. Also, this method lends itself to automation and less labor-intensive typing.

Restriction Fragment Length Polymorphism Analysis (RFLP): a technique that uses probes to detect variation in a DNA sequence according to differences in the length of DNA fragments that are created using specific enzymes. These enzymes act like microscopic scalpels and cut the DNA strands at specific points, producing fragments that can be analyzed. The combination and number of chemical repeats within each particular sequence determine the size of the fragment and the differences among individuals. RFLP was used predominantly by DNA laboratories until newer technology was developed. In the past, it could take as long as a couple of weeks to obtain results using RFLP. It requires the use of a sizeable amount of good quality DNA.

State DNA Index System (SDIS): contains the state-level DNA records uploaded from LDIS sites within the state. SDIS is the state's repository of DNA identification records and is under the control of state authorities. The SDIS laboratory serves as the central point of contact for access to NDIS.

Short Tandem Repeats: short repeating units of identical chemical sequences arranged in direct succession in a particular region of the DNA.

Short Tandem Repeat Analysis (STR): refers to a DNA typing method that utilizes PCR technology to quickly amplify and analyze sections of DNA that contain short tandem repeats. The number of repeated sequences in specific portions of the DNA varies from person to person. This method allows a high level of discrimination, since 13 loci are examined and subsequently compared with other samples. STR also requires considerably less time and less DNA than the RFLP technology.