Criticisms were raised concerning the reliability of the technical methods, including the criteria for identifying DNA patterns and declaring matches, as well as quality control.
Questions were raised about the validity of estimates of probability of random inclusion that were being presented in courts. Were the individual components of a specific DNA pattern statistically independent, so that it was proper to multiply their frequencies together in calculating the chance of a match? What population databanks were appropriate?
Because DNA can be used to derive medical and other personal information, questions of confidentiality and privacy have assumed greater importance in DNA typing than in the use of non-DNA tests.
By the summer of 1989, because of questions concerning DNA typing raised in connection with some well-publicized criminal cases, the scientific and legal communities had called for an examination of the issues by the National Research Council of the National Academy of Sciences.5,7,8 As a response, the Committee on DNA Technology in Forensic Science was formed, and its first meeting was held in January 1990. The committee was to address the general applicability and appropriateness of the use of DNA technology in forensic science, the need for standards in data collection and analysis, the need for advances in technology, management of DNA typing data, and legal, societal, and ethical issues surrounding DNA typing.
Genetics is the science of biological variation. The fundamental basis of genetics and the essence of Mendel's discovery in 1865 is that inheritance is particulate and that the inherited factors (genes) that determine visible traits exist in pairs of alleles (i.e., alternative forms of a gene at a given site)—one on a chromosome inherited from the father and one on a chromosome from the mother. Chromosomes that contain genes are threadlike or rodlike structures in the cell nucleus. An organism's particular combination of alleles is referred to as the organism's genotype; the collection of traits resulting therefrom is referred to as the organism's phenotype. Most markers (i.e., identifiable physical locations on a chromosome) used in forensic DNA typing are not parts of expressed genes (i.e., genes that code for products like proteins); they are in noncoding portions of DNA. Hence, they are not associated with a phenotype.
A trait that differs among individuals is referred to as a polymorphism.9 In DNA typing, that term is used interchangeably with "variation." The variations in blood groups, serum protein types, and HLA tissue types used for forensic testing in the pre-DNA era were polymorphisms in the protein product; these proteins contain variations that reflect variations in DNA. But DNA technology makes it possible to study the variations directly.