Justice and Science: Trials and Triumphs of DNA Evidence

Glossary

195 ABO blood grouping Blood typing system used to determine differences that exist among humans in blood and, in most persons , other body fluids. Most common types are A, B, AB, and O. adenine (A) One of the four nucleotides, or bases, that are the building blocks of DNA. Pairs with thymine (T) in DNA in its normal state. allele Form, or type, at a single location (locus) of DNA. One allele is inherited from each parent at a single DNA locus. amplification The process of copying portions, or segments, of DNA using the polymerase chain reaction. autoradiograph Most commonly, X-ray depiction of the relative positions of DNA segments following the use of the RFLP testing process. base A nucleotide that together with its complementary nucleotide forms a base pair, which is a basic building block of DNA. biological evidence Evidence consisting of body fluid, organ, or other tissue normally containing DNA. ceiling principle Mathematical formula suggested in 1992 National Research Council report, DNA Technology in Forensic Science. Promulgated to provide an alternative approach to the use of the unmodified product rule for statistical estimates of the rarity of matching DNA profiles. Glossary R4400.indb 195 R4400.indb 195 8/24/07 11:46:56 AM 8/24/07 11:46:56 AM 196 Glossary cell Smallest unit of an organism that can function on its own. Cells with a nucleus contain DNA that can be tested for DNA profiles. chain of custody The description and documentation of the collection, preservation, and movement of evidence. chromosome Structure by which DNA is transmitted to each succeeding generation. Contains a single DNA molecule . When all twenty-three chromosomes are present in pairs, they make up the entire human DNA complement. CODIS Also known as the Combined DNA Index System. The FBI computerized system software linking national , state, and local DNA database systems. cold hit A computer match of the DNA profile of evidence in an unsolved case and the DNA profile either of a convicted offender or of evidence in another case. contamination Normally, the inadvertent transfer of DNA to an evidence item or other sample in a case. control A sample used to help ensure the accuracy of DNA or serological profiles determined from evidentiary and known samples. Controls may be positive or negative. They help reveal any irregularities in DNA testing procedures. cytoplasm The area inside a cell but outside the nucleus. Contains the mitochondria that can be tested for mitochondrial DNA. cytosine (C) One of the four nucleotides, or bases, that are the building blocks of DNA. Pairs with guanine (G) in DNA in its normal state. degradation The process during which DNA breaks up; it ultimately prevents the determination of DNA profiles. DNA Deoxyribonucleic acid. The molecule containing genetic information, which is transmitted through reproduction . Determines the structure and regulates the functioning of humans, animals, and other living organisms. DQ-Alpha First genetic marker, or locus, tested following polymerase -chain-reaction amplification of samples to R4400.indb 196 R4400.indb 196 8/24/07 11:46:56 AM 8/24/07 11:46:56 AM 197 Glossary detect differences among people and to compare evidence samples in criminal cases. electrophoresis Physical process that permits the separation for typing of segments of DNA, as well as of serological proteins and enzymes. enzyme A protein that causes biological functions, such as human digestion, to take place. Certain enzymes can be tested using serological techniques to determine differences among people. epithelial cells Cells that provide a surface coating on body structures . Commonly found in saliva, vaginal secretions, and other mucous-membrane fluids. exclusion The determination by DNA or serological typing that a specific person could not be the donor of a sample of biological evidence. forensic hit A computer match of the DNA profile of evidence in an unsolved case and the DNA profile of evidence in another case. forensic science The application of science to the legal system. gene The basic unit of heredity. A portion of a DNA chromosome that governs a specific function of the body or provides a product for its use. In serological or DNA testing, a location where DNA differences among humans has been determined. genetic marker A gene or location (locus) where DNA or serological types can be determined. genotype The types (alleles) inherited from a person’s mother and father at a specific location or genetic marker. guanine (G) One...