Familial DNA Searching

Nowadays, DNA is a crucial component of a crime scene investigation, used to both to identify perpetrators from crime scenes and to determine a suspect’s guilt or innocence (Butler, 2005). The method of constructing a distinctive “fingerprint” from an individual’s DNA was first described by Alec Jeffreys in 1985. He discovered regions of repetitions of nucleotides inherent in DNA strands that differed from person to person (now known as variable number of tandem repeats, or VNTRs), and developed a technique to adjust the length variation into a definitive identity marker (Butler, 2005). Since then, DNA fingerprinting has been refined to be an indispensible source of evidence, expanded into multiple methods befitting different types of DNA samples. One of the more controversial practices of DNA forensics is familial DNA searching, which takes partial, rather than exact, matches between crime scene DNA and DNA stored in a public database as possible leads for further examination and information about the suspect. Using familial DNA searching for investigative purposes is a reliable and advantageous method to convict criminals.

Familial DNA searching works by using the combined DNA index system (CODIS) to compare DNA samples taken from crime scenes to DNA profiles already recorded in the local, state, or national criminal DNA database. There are many indexes in the database; two of the largest are the offender index, a catalogue of DNA profiles from previously convicted felons, and the forensic index, a catalogue of DNA from crime-scenes. A DNA sample is run through the database by CODIS’ matching algorithm that searches the indexes against one another to generate matches according to how often base pairs, or “markers,” repeat in th...

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...of Justice, 1 Sept. 2011.

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