CHAPTER 11 of A Judge's Deskbook on the Basic Philosopies and Methods of Science, by Shirley A. Dobbin, Ph.D, and Sophia I. Gatowski, Ph.D DNA Evidence
For all the diversity of the world's five and a half billion people, full of creativity and contradictions, the machinery of every human mind and body is built and run with fewer than 100,000 kinds of protein molecules. And for each of these proteins, we can imagine a single corresponding gene (though there is sometimes some redundancy) whose job it is to ensure an adequate and timely supply. In a material sense, then, all of the subtlety of our species, all of our art and science, is ultimately accounted for by a surprisingly small set of discrete genetic instructions. More surprisingly still, the differences between two unrelated individuals, between the man next door and Mozart, may reflect a mere handful of differences in their genomic recipes - perhaps one altered word in five hundred. We are far more alike than we are different. At the same time, there is room for near-infinite variety. It is no overstatement to say that to decode our 100,000 genes in some fundamental way would be an epochal step toward unraveling the manifold mysteries of life.(1) Advances in molecular biology have spawned a host of new tests for criminal identification and paternity assessment. Because they examine variations in human DNA, the new tests are generally called "DNA tests" or "DNA typing procedures." These labels cover a variety of different methods, however, and different methods for "typing" DNA can vary in their reliability, specificity, and appropriateness for particular applications.(2) \The fundamental science underlying forensic DNA tests is not in dispute. There is no question, for example, that genetic differences exist among individuals and that DNA tests can uncover those differences. Disputes have arisen, however, about whether particular procedures have been adequately validated, whether laboratories are using adequate standards and controls to ensure the reliability of tests, and whether the results in particular cases have been interpreted correctly. Disputes have also arisen about the validity and appropriateness of methods used to characterize the statistical meaning of a DNA match and, more generally, about the appropriate way to present DNA test results to juries. Moreover, as genetic research advances, and geneticists and biochemists come increasingly closer to mapping the human genome, the court, and society as a whole, must come to terms with challenging social, moral, and legal issues. The origins of genetic research can be traced back centuries when farmers began breeding domestic animals and crops to achieve the desired characteristics for productivity and durability. Observations of how physical characteristics (phenotype) could be manipulated led to the work of Gregor Mendel, an Austrian monk, who came to be known as the "Father of Genetics" for his work on genetics in the nineteenth century. In the first half of the twentieth century, through the efforts of James Watson and Francis Crick, genetics was linked to DNA. By discovering the double helix structure of DNA (i.e., two DNA strands are twisted together into an entwined spiral), Watson and Crick revolutionized genetics. DNA analysis is based on well-established principles of the wide genetic variability among humans and the presumed uniqueness of an individual's genetic makeup (identical twins excepted). Laboratory techniques for isolating and observing the DNA of human chromosomes have long been used in non-forensic scientific settings. The forensic application of the technique involves comparing a known DNA sample obtained from a suspect with a DNA sample obtained from the crime scene, and often with one obtained from the victim. Such analyses typically are offered to support or refute the claim that a criminal suspect contributed to a biological specimen (e.g., semen or blood) collected at the crime scene. Other considerations may arise where DNA is used to narrow the field of suspects by comparing a crime sample with samples from a blood bank, to establish the commission of a crime where no body is found, and to establish parentage.	Learning Objectives for Chapter 11 Upon completion of this chapter, the reader should be able to: Understand the basic theory of molecular biology; Articulate some of the social, moral, and legal questions surrounding breakthroughs in genetic research; Understand DNA testing concepts; Identify the controversies surrounding laboratory protocols, population databases, and the possibility of errors; and Understand the courts' reaction to DNA evidence. Mapping the Human Genome The Human Genome Project (HGP) is a multi-national project involving sixteen nations. The United States has worked most closely with Great Britain, France, and Japan. In the U.S., the project is funded by the National Institutes of Health (through the National Center for Human Genome Research) and the Department of Energy (through the Human Genome Project). The effort was expected to cost approximately $3 billion and to take about 15 years, but the project is progressing ahead of schedule. It is now generally agreed that this international project will produce the complete sequence of the human genome by the year 2005. The first goal of the project is to discover and map all 50,000 to 100,000 human genes, which together make up the human genome, and to make the human genome itself accessible for biological study. Current and future applications of genome research will address national needs in molecular medicine, waste control and environmental cleanup, biotechnology, energy sources, and risk assessment. Breakthroughs in genetic research will change our understanding of ourselves and our families, and the meaning of health and illness.
Before going any further, stop and reflect ... The social, moral, and legal issues raised by modern genome research are possibly among the most challenging ever faced &endash; by the courts and by society as a whole. For example, one of the primary goals of genetic research is finding the genetic basis of diseases which will ultimately lead to therapies and interventions that will relieve human suffering. Emphasis will shift from treatment of the sick to a prevention-based approach. Researchers will be able to identify individuals predisposed to, or at risk for, particular diseases and will be able to provide novel therapeutic regimens based on new types of drugs, immunotherapy techniques, and the possible replacement of defective genes through gene therapy. How might increased genetic information change our current understanding of "health," "illness," and "disease"? How might increased genetic information change our current notion of "family" and "self"? What legal issues do you see arising from increased genetic information? Consider: privacy and confidentiality; informed consent; discrimination; insurance coverage; adoption; and fairness in risk assessment. Is the court, and the judiciary, ready to deal with these issues? Can human beings be entrusted with the control of their own inheritance? For a good overview of some of these issues see: Furrow et al (1998). "Legal, Social and Ethical Issues in Human Genetics." Bioethics and the Law, West Publishing, pps 150-178.	A national snapshot of judges experience with DNA evidence ... Although 34% of judges surveyed had no experience with DNA evidence in the courtroom, 76% of those judges who reported that they had had experience with DNA evidence were only somewhat familiar with the methods and procedures of DNA analysis. Of those judges reporting experience with DNA evidence, 26% noted that the most common type of case involving a proffer of DNA was a sexual assault case. 24% reported that the most common cases proffering DNA evidence, in their experience, were cases where paternity of a child is at issue. 14% of judges saw DNA evidence proffered most often in criminal homicide cases.
What Comprises DNA?(3) DNA, or deoxyribonucleic acid, is often called the blueprint of life. It contains all the genetic material that comprises an individual and makes that individual unique. DNA is a double-stranded molecule that contains the genetic code. DNA is composed of 46 rod-shaped chromosomes; 23 of which are inherited from the mother and 23 of which are inherited from the father. Each chromosome has the shape of a double-helix, as first described in 1952 by scientists James Watson and Francis Crick. A piece of a chromosome that dictates a particular trait is called a gene. Genes are the fundamental units of heredity. Collectively, the genes of an organism inform nearly every aspect of the development and formation of that organism. A gene is found at a particular site, or locus, on a particular chromosome. Each distinctive sequence or configuration that may be found is an allele. Normal individuals have two copies of each gene at a given locus -- one from the father and one from the mother. Consequently, at each locus examined by DNA tests, a person typically has two alleles, one maternal and one paternal. This pair of alleles is a genotype. A locus on a DNA molecule where all humans have the same genetic code is called monomorphic. However, genes vary. An individual may receive the genetic code for blue eyes from her mother and the genetic code for brown eyes from her father. A locus where the allele differs among individuals is called polymorphic, and the difference is known as polymorphism. The set of genotypes possessed by a person at two or more loci is a multi-locus genotype or DNA profile. Structurally, DNA is a double helix -- two strands of genetic material spiraled around each other. Each strand has a "backbone" made of sugar and phosphate groups and a sequence of nitrogenous bases, also called nucleotides, attached to the sugar groups. A base is one of four chemicals (adenine, guanine, cytosine and thymine). The two strands of DNA are connected at each base. Each base will only bond with one other base, as follows: Adenine (A) will only bond with thymine (T), and guanine (G) will only bond with cytosine (C). Code messages (genes) are stored along a chromosome in sequences of these chemical bases. These linkages, called base pairs, are the identification guide for DNA. The human genome is comprised of about three billion base pairs. The chemical structure of everyone's DNA is the same. The only difference between people (or any animal) is the order of the base pairs. There are so many millions of base pairs in each person's DNA that every person has a different sequence. Using these sequences, every person could be identified solely by the sequence of their base pairs. However, because there are so many millions of base pairs, the task would be very time-consuming. Instead, because of repeating patterns in DNA, scientists are able to use a shorter method. These patterns do not, however, give an individual "fingerprint," rather, they are able to determine whether two DNA samples are from the same person, related people, or non-related people. Scientists use a small number of sequences of DNA that are known to vary among individuals a great deal, and analyze those to get a certain probability of a match. DNA tests are useful for identification because DNA profiles are highly variable across different people, making it unlikely that two different people will happen to have exactly the same profile. Of course, DNA profiles are not necessarily unique because different individuals may, by chance, have the same genotypes in one or more loci. The likelihood of such a chance similarity depends on both the rarity of the matching genotype at each locus and the number of loci examined.	DNA (Deoxyribonucleic Acid): a double-stranded molecule that contains the genetic code; composed of 46 rod-shaped chromosomes; 23 of which are inherited from the mother and 23 of which are inherited from the father Chromosome: a threadlike structure that carries genetic information arranged in a linear sequence; in humans, it consists of a complex of nucleic acids and proteins Gene: the fundamental unit of heredity; an ordered sequence of nucleotide base pairs to which a specific production or function can be assigned Locus: a specific, physical location on a chromosome Allele: alternative form of a genetic locus (e.g., at a locus for eye color there might be alleles resulting in blue or brown eyes); alleles are inherited separately from each parent Genotype: the genetic constitution of an organism Monomorpic: a locus on a DNA molecule where all humans have the same genetic code Polymorphic: the existence of more than one form of a genetic trait DNA Profile: the set of genotypes possessed by a person at two or more loci is a multi-locus genotype or DNA profile Nucleotide: the unit of DNA consisting of one of four bases - adenine, guanine, cytosine, or thymine -attached to a phosphate-sugar group Suppose one strand of DNA looks like this: A-A-C-T-G-A-T-A-G-G-T-C-T-A-G The DNA strand bound to it will look like this: T-T-G-A-C-T-A-T-C-C-A-G-A-T-C Together, the section of DNA would be represented like this: T-T-G-A-C-T-A-T-C-C-A-G-A-T-C A-A-C-T-G-A-T-A-G-G-T-C-T-A-G
Forensic Use vs. Paternity Case Use of DNA Comparisons DNA is used differently in forensic cases than in paternity cases. In the paternity case, there is no need to use a population database, as there is with forensic DNA testing. In criminal cases, the DNA is extracted from blood or tissue at the scene without the knowledge of whose DNA it is. The laboratory then uses statistics to determine the probability that the DNA found at the scene matches the known sample of the suspect's DNA. This is not done in paternity cases. Instead, the DNA from the child is compared to the parents' DNA to determine the likelihood of paternity by the probability that certain genetic markers would show up in the child's DNA.	DNA testing in paternity cases involves comparing DNA from a child to the parents DNA to determine the likelihood of paternity by the probability that certain genetic markers would show up in the childs DNA; there is no need to use a population database
Making a DNA Print There is currently more than one method of obtaining a DNA profile, but basically the process can be simplified as follows: 1. Collect the sample: DNA is extracted from traces of blood, semen, saliva, urine, hair roots, or bone - wherever nucleated cells are found. 2.Extract and purify DNA: The sample of DNA is treated with chemicals to break open the cells. In a centrifuge, DNA is separated from the cells and later purified. 3. Cut DNA into fragments: Enzymes that recognize certain sequences in the chemical base patterns are added to the DNA. These enzymes, proteins that cause a chemical reaction, act like molecular scissors and cut the DNA molecule at specific points, leaving fragments of various lengths. This process is known as restriction enzyme analysis. These restriction enzymes recognize a specific sequence normally of four to six bases in size. This target sequence will occur at various frequencies in different DNA molecules (i.e., different individuals) but will have the same number and location within identical DNA molecules (i.e., same individual). This allows DNA to be "cut" into repeatable and recognizable patterns of specific size fragments. 4. Sort fragments by length: The DNA fragments are placed on a bed of gel, and an electric current is applied. The DNA, which is negatively charged, moves towards the positive end. Several hours later the fragments have become arranged by length. This process is known as gel electrophoresis. Once the electrophoresis is complete the gel can be stained to allow visualization of the molecules. 5. Split and transfer DNA: Alkaline chemicals are introduced to split the DNA fragments apart. At the same time, a nylon sheet is placed over the gel and covered with layers of paper. The process, known as Southern blotting (named after its inventor) allows transfer of molecules (separated by size and/or charge) from a fragile semisolid gel to a membrane matrix. Following transfer to the membrane, the molecules can be subjected to a variety of different tests which can provide information concerning their quantity, genetic relatedness, size, etc. 6. Hybridization: Hybridization is the coming together, or binding, of two genetic sequences. The binding occurs because of the hydrogen bonds between base pairs. Between an A base and a T base, there are two hydrogen bonds; between a C base and a G base, there are three hydrogen bonds. When making use of hybridization in the laboratory, DNA must first be denatured (unzipped), usually by using heat or chemicals. Denaturing is a process by which the hydrogen bonds of the original double-stranded DNA are broken, leaving a single strand of DNA whose bases are available for hydrogen bonding. Once the DNA has been denatured, a single-stranded radioactive probe can be used to see if the denatured DNA contains a sequence similar to that on the probe. The denatured DNA is put into a plastic bag along with the probe and some saline liquid; the bag is then shaken to allow sloshing. If the probe finds a fit, it will bind to the DNA. 7. Make a print and analyze it: X-ray film is exposed to the nylon sheet containing the radioactive probes. Two dark bands develop at the probe sites. If an X-ray is taken of the blot after a radioactive probe has been allowed to bond with the DNA on the paper, only the areas where the radioactive probe binds will show up on the film. This picture is termed an autoradiogram, and allows researchers to identify, in a particular person's DNA, the occurrence and frequency of the particular genetic pattern contained in the probe.	Restriction Enzyme: an enzyme normally found in bacteria which cuts DNA at specific sites; because a restriction enzyme always acts upon DNA in the same manner, a map can be made of a restriction enzymes actions on a known set of molecules Gel Electrophoresis: technique used to separate molecules such as DNA fragments or proteins; in forensic uses of DNA tests, electric current is passed through a gel, and the fragments of DNA are separated by size; smaller fragments will migrate farther than larger pieces Southern Blotting: the transfer of molecules which have been separated by electrophoresis from the gel onto a membrane (named for the inventor) Hybridization: the process of joining two complementary strands of DNA, or of DNA and RNA, together to form a double-stranded helix Denaturing: a process by which the hydrogen bonds on the original double-stranded DNA are broken, leaving a single strand of DNA whose bases are available for hydrogen bonding Probe: short segment of DNA that is labeled with a radioactive or other chemical tag and then used to detect the presence of a particular DNA sequence through hybridization to its complementary Autoradiogram: an x-ray film image showing the position of radioactive substances; sometimes called an autorad
The PCR Analysis Method Polymerase Chain Reaction (PCR) is an amplification technique used when the DNA sample is small or when the sample is degraded by chemical impurities or damaged by environmental conditions. It is a process that yields copies of desired DNA through repeated cycling of a reaction that involves the enzyme DNA polymerase. This process mimics the DNA's own replication process in order to make up to millions of copies of the original genetic material in only a few hours. Although PCR is only an amplification technique, PCR is commonly used to describe an alternative analysis technique for testing for the presence of matching alleles. Instead of measuring the length of DNA fragments, allele-specific probes are used to determine whether a specific allele is present. The usual format for the use of these probes is to introduce them onto a nylon membrane where the PCR has already been placed. This method is called 'dot blotting' because the samples are spotted as 'dots' on the membrane. An alternative method is called 'reverse dot blotting' because instead of introducing probes onto a strip of PCR product strands, strands of probes are immobilized on a test strip and the test strip is then immersed in the PCR product solution, causing the PCR product to hybridize only to its complementary probe. In the allele-specific technique, the spots where DNA fragments have combined indicate a 'yes' answer - the targeted alleles are present. If the types do not match, the next step is to perform a statistical analysis of the population frequency of the allele types to determine the probability of such a match being observed by chance in a comparison of samples from different persons.	Polymerase Chain Reaction (PCR): an amplification technique used when the DNA sample is small or when the sample is degraded by chemical impurities or damaged by environmental conditions
VNTR Profiling Every strand of DNA has pieces that contain genetic information which informs an organism's development (exons) and pieces that, apparently, supply no relevant genetic information at all (introns). Although the introns may seem useless, it has been found that they contain repeated sequences of base pairs. These sequences, called Variable Number Tandem Repeats (VNTRs) can contain anywhere from twenty to one hundred base pairs. Every human being has some VNTRs. To determine if a person has a particular VNTR, a Southern blot is performed, and then the Southern blot is probed, through a hybridization reaction, with a radioactive version of the VNTR in question. The pattern which results from this process is what is often referred to as a DNA fingerprint. A given person's VNTRs come from the genetic information donated by her parents; she could have VNTRs inherited from her mother or father, or a combination, but never a VNTR that neither of her parents had. Because VNTR patterns are inherited genetically, a given person's VNTR pattern is more or less unique. The more VNTR probes used to analyze a person's VNTR pattern, the more distinctive and individualized that pattern, or DNA fingerprint, will be.(4)	Variable Number Tandem Repeats (VNTRs): repeated sequences of base pairs found in every strand of DNA
Applications of DNA Testing Paternity and Maternity: Because a person inherits his VNTRs from his parents, VNTR patterns can be used to establish paternity and maternity. The patterns are so specific that a parental VNTR pattern can be reconstructed even if only the children's VNTR patterns are known (the more children produced, the more reliable the reconstruction). Parent-child VNTR pattern analysis has been used to solve standard father-identification cases as well as more complicated cases of confirming legal nationality and, in instances of adoption, biological parenthood. Criminal Identification and Forensics: DNA isolated from blood, hair, skin cells, semen, or other genetic evidence left at the scene of a crime can be compared, through VNTR patterns, with the DNA of a criminal suspect to determine guilt or innocence. VNTR patterns are also useful in establishing the identity of a homicide victim, either from DNA found as evidence or from the body itself. Personal Identification: The notion of using DNA fingerprints as a sort of genetic bar code to identify individuals has been discussed, but this is not likely to happen anytime in the foreseeable future. The technology required to isolate, keep on file, and then analyze millions of very specified VNTR patterns is both expensive and impractical. Social security numbers, picture ID, and other more mundane methods are much more likely to remain the prevalent ways to establish personal identification.
Potential Sources of Error in DNA Testing Evidence samples are sensitive to mixture and contamination (e.g., samples might contain a mixture of DNA from multiple sources and might be contaminated with chemicals that can interfere with the analysis) 'Band Shifting': DNA samples may migrate at different speeds and yield shifted patterns &endash; 'band shifting' could cause two DNA samples from the same person to show The possibility of human error exists at every stage of the process &endash; if an analyst refuses to declare a match unless the DNA prints are identical in all respects, the declared non-match could result in false negatives (i.e., two samples of DNA may actually come from the same individual but the prints are interpreted as a negative match)
Using DNA Profiles for Comparison Simply making a DNA profile is not useful without a means of comparison to other known (or unknown) samples. The essence of this process is to measure the bands from both samples and compare them. In order to declare a match, the bands do not need to line up exactly, but need to fall within a certain distance of one another. The acceptable deviation rate varies from one laboratory to another. The issue of matching DNA profiles has caused some debate in the scientific community. There have been complaints that the standards by which a match is declared are not objective and that there is often too much interpretation of data when a match is declared. If no match has been declared between the known sample and the sample in question, then the inquiry ends there. Likewise, if the sample in question was contaminated, no match will be declared and the inquiry ends there. However, if a match is declared, the next step is to determine what, if any, meaning that match has. The question as to whether the match has any meaning arises because unless one knows how common such a match would be, the importance of the match is unknown. If a profile match is declared, it means only that the DNA profile of the suspect is consistent with that of the source of the crime sample. The crime sample may be from the suspect or from someone else whose profile, using the particular probes involved, happens to match that of the suspect. Expert testimony concerning the frequency with which the observed alleles are found in the appropriate comparison population is necessary for the finder of fact to make an informed assessment of the incriminating value of this match. The frequency with which an individual allele occurs in the comparison population is taken to be the probability of a coincidental match of that allele. These individual probabilities of a coincidental match are combined in an estimate of the probability of a coincidental match on the entire profile.	Statistical Calculations Used In DNA Testing Population Genetics In determining the probability of a certain DNA profile being the same as a profile in question, experts use a previously constructed database developed by the laboratory. Databases are generally divided into broad racial classification and each database is composed of the DNA of a few hundred people. In that database, the experts find and extract specific polymorphic alleles from known sites and calculate the odds from those alleles. Thus, allele A may be found in 1 in 10, allele B may be found in 1 in 20, allele C is 1 in 5, and allele D is one in 100. If there are sites A, B, C, and D, the sample in question must match the known sample in those four sites in order for there to be a match. The expert then calculates the odds of that match. The Product Rule In order to calculate the odds of the match being from the same sample, the product rule is employed. The odds of the first sample are multiplied with the odds of the second, the third and the fourth (e.g., 1/10 x 1/20 x 1/5 x 1/100 = 1/100,000). Thus, the odds of a match are one in 100,000 that the person in question has the same genetic profile as the sample taken from the scene.
Problems with Determining Probability VNTRs, because they are results of genetic inheritance, are not distributed evenly across all of the human population. A given VNTR cannot, therefore, have a stable probability of occurrence; it will vary depending on an individual's genetic background. The difference in probabilities is particularly visible across racial lines. Some VNTRs that occur very frequently among Hispanic Americans will occur very rarely among Caucasians or African Americans. Currently, not enough is known about the VNTR frequency distributions among ethnic groups to determine accurate probabilities for individuals within those groups; the heterogeneous genetic composition of interracial individuals, who are growing in number, presents an entirely new set of questions. Further experimentation in this area, known as population genetics, has been surrounded with and hindered by controversy, because the idea of identifying people through genetic anomalies along racial lines comes alarmingly close to the eugenics and ethnic purification movements of the recent past, and, some argue, could provide a scientific basis for racial discrimination. Errors in the hybridization and probing process must also be figured into the probability, and often the idea of error is not acceptable. Most people will agree that an innocent person should not be sent to jail, a guilty person allowed to walk free, or a biological mother denied her legal right to custody of her children, simply because a lab technician did not conduct an experiment accurately. When the DNA sample available is minuscule, this is an important consideration, because there is not much room for error, especially if the analysis of the DNA sample involves amplification of the sample (creating a much larger sample of genetically identical DNA from what little material is available). That is, if the wrong DNA is amplified (e.g., a skin cell from the lab technician) the consequences can be profoundly detrimental.	Areas of Controversy in Statistical Calculations Used in DNA Testing The possibility of false assumptions --What if the profile for allele D shows up in 1 out of 100 of the individuals in the database but in real life shows up in 1 out of 20 people? Problems like this can arise because the databases used by the laboratories are small. Also, the design of the database may create errors. For example, the Native American database referred to in the case of Springfield v. State (860 P.2d 435, Wyo. 1993) was composed of 200 individuals from the Navajo, Cherokee, and Cheyenne nations. The individual in question, however, was a member of the Crow tribe, which was not represented in the database at all. The 'linkage equilibrium' problem -- Scientists must be sure when designing DNA studies that the alleles to be tested are truly unrelated, because the product rule is accurate only when the variables are independent of one The 'Hardy-Weinberg equilibrium problem' -- The basis for statistical calculations in population genetics rests on the belief in a truly random population (i.e., a population that mates randomly and thus mixes the gene pool evenly).
The Ceiling Principle and the Modified Ceiling Principle In the late 1980s and early 1990s there was a debate over the significance of random mating in the construct of the database (i.e., the Hardy-Weinberg equilibrium problem). A compromise position commonly termed the 'ceiling principle' or 'modified ceiling principle' was proposed as a useful and conservative method for calculating statistical probabilities. The ceiling principle approach incorporates into the calculation "the greatest observed frequency of particular alleles within a given number of randomly selected population groups."(5) To determine ceiling frequencies, random samples of 100 persons from each 15-20 populations that represent groups relatively homogenous genetically are drawn. Then, either the largest frequency of those populations or 5%, whichever is larger, is taken as the ceiling frequency.(6) In some areas, the 'modified ceiling principle' has been used. This method uses a 10% frequency for each allele or, if it is higher, the highest frequency found for an allele among the laboratory's broad racial databases.(7) Beginning in 1994, the scientific landscape started shifting on the issues surrounding population restructuring. Now, scientists are concluding that these issues should not have a significant impact on final calculations. Stating that the "DNA wars are over," they have come out in favor of using the product rule and no longer requiring the ceiling or modified ceiling principle.(8) The areas of continuing concern with respect to DNA testing are on a case-by-case basis, where the validity of individual results will be challenged. Rather than the initial concerns about population substructure, the newest concerns with respect to DNA evidence center around the possibility of error in laboratories. Who are the Relevant Scientific Communities? Most courts have accepted molecular biologists as the relevant scientific community with respect to laboratory techniques of isolating and probing the DNA. The statistical interpretation of the results has been more properly the province of population geneticists. Individuals from other fields, such as genetic epidemiology and biostatistics, also may have the requisite background to testify about analysis. Forensic scientists or laboratory technicians involved in the analysis often do not have a strong background in the relevant scientific discipline but may be knowledgeable about techniques of sample collection and preservation, forensic laboratory standards and procedures, and proficiency tests.	Determining the admissibility of DNA evidence Judges who reported that they had experience with DNA evidence in the courtroom were also asked what factors they considered when determining the admissibility of such evidence. These judges reported the following factors as important considerations (in order of frequency of mention): the way the DNA sample was obtained, gathered, or preserved the qualifications of the expert the status of the laboratory the general acceptance of DNA evidence generally the reliability of the testing procedure When judges who reported that they had experience with DNA evidence in the courtroom were asked what aspect of such evidence is most problematic in determining its admissibility, the following factors were identified (in order of frequency of mention): determining how the sample was obtained, gathered or preserved the statistical basis of the conclusions drawn determining how the sample was tested determining the reliability of the testing procedure
Issues Pertaining to Sample Quantity and Quality(9) Several factors may affect a DNA sample's suitability for analysis. For each factor claimed to affect a particular analysis, the court may want to have the expert address whether its influence is likely to cause a false positive result (incorrect identification of the suspect as a potential source of the forensic DNA) or merely an inconclusive or uninterpretable result. Did the Crime Sample Contain Enough DNA to Permit Accurate Analysis? To be interpretable, the crime sample must contain enough DNA of sufficiently high molecular weight to allow isolation of longer DNA fragments, which are the most susceptible to degradation. Samples of blood, semen, or other DNA sources may be too small to permit analysis. To the extent that small sample size precludes a full series of tests (three to five probes), it can significantly diminish the power of the DNA testing procedure to distinguish between DNA samples obtained from different individuals. In addition, the unavailability of additional DNA precludes repeated testing that might verify or refute the initial test. Was the Crime Sample of Sufficient Quality to Permit Accurate Analysis? Exposure to heat, moisture, and ultraviolet radiation can degrade the DNA sample. Samples may also have been contaminated by exposure to chemical or bacterial agents that alter DNA, interfere with the enzymes used in the testing process, or otherwise make DNA difficult to analyze. Such exposure is known as an 'environmental insult.' Although old samples of DNA may be analyzed successfully, attention must be given to possible sample degradation due to age. How Many Sources of DNA are Thought to be Represented in the Crime Sample? Often, the expected composition of a crime sample of DNA can be narrowed to a single perpetrator, or single victim, or both. However, a crime sample may be thought to include DNA from multiple sources, as when more than one person is thought to have contributed to the crime sample of blood or semen. Male and female DNA extracted from such a sample may be distinguished, as can same-sex DNA where the alternative sources areis known and available for testing (e.g., a rape victim's husband). The presence of multiple, same-sex samples from unknown sources adds additional complications. Mixed samples can be difficult to interpret, although the intensity of the different bands can offer clues.	Laboratory Standards Laboratories must maintain appropriate documentation on all significant aspects of the DNA analysis procedure, as well as any related documents or laboratory records that are pertinent to the analysis or interpretation of results. Laboratory procedures must be validated. Guidelines stress the importance of validation to acquire the necessary information to assess the ability of a procedure to reliably obtain a desired result, determine the conditions under which such results can be obtained, and determine the limitations of the procedure. Laboratories must have been subjected to appropriate proficiency testing, preferably by an independent institution. Questions to consider when evaluating DNA testing procedures Was the crime scene contaminated? Was the sample too small for proper testing? Was there destruction of the sample? What about the problem of shifting bands? What about the possibility of false assumptions? Were poor quality laboratory procedures used? Was the population database too small or not appropriately used?
Some Case Law on DNA The science of DNA fingerprinting changes rapidly. As the science has changed, so have the courts decisions on whether to admit expert testimony. Following the 1992 NRC Report, a number of courts embraced the ceiling principle and modified ceiling principle. Since that time however, scientists appear to have reached agreement that the product rule provides a more accurate analysis and that there is no need to use the ceiling principle. This change in position has been recognized by a number of courts across the country (e.g., State v. Johnson, 922 P.2d 294, Ariz. 1996; Clark v. State, 679 So.2d 321, Fla. App. 1996; State v. Marcus, 683 A.2d221, N.J. Super. 1996). Furthermore, several courts have eliminated the use of any of the ceiling principles, deciding that the product rule provides a proper basis for statistical analysis (e.g., People v. Pope, 672 N.E.2d 1321, Ill. App. 1996; Armstead v. State, 673 A.2d 221, Md. 1996; People v. Freeman, 571 N.W.2d 276, Neb. 1997). In March 1998 the Supreme Court of Arizona decided that PCR testing was admissible, after finding that it met the Frye standard of scientific admissibility (State v. Tankersley, 1998 WL 107864, Ariz. 1998). The court noted that the overwhelming consensus among scientists is that so long as proper procedures are followed, the results should be reliable (at 5). Arizona is not alone in its acceptance of either the PCR method of testing DNA or the admissibility of DNA evidence without the use of ceiling principles. In State v. Stills, the Supreme Court of New Mexico approved of the method, quoting a commentator who stated that PCR analysis has received overwhelming acceptance in the scientific community and the courts (957 P.2d 51, N.M., 1998 at 4). A number of courts, both state and federal, have held PCR evidence admissible (e.g., Brodine v. State, 936 P.2d 545, Alaska App. 1997; State v. Isley, 936 P.2d 275, Kan. 1997; State v. Harvey, 699 A.2d 596, N.J. 1997; State v. Begley, 956 S.W.2d 471, Tenn. 1997; United States v. Lowe, 954 F. Supp. 401, D. Mass. 1996). Since 1990, a number of states have enacted statutes governing the admissibility of DNA evidence. Virginia, for example, enacted a statute providing that DNA testing shall be deemed to be a reliable scientific technique and the evidence of a DNA profile comparison may be admitted to prove or disprove the identity of any person (Va Code 19.2-270.5; see also Md Cts & Jud Proc Code 10-915; Minn Stat 634.25, 634.26; Wash Rev Code 43.43.752 through 43.43.758; and La Rev Stat 15.441.1).
Before going any further, stop and reflect ... How is the evaluation of DNA evidence and testing procedures like or unlike other forms of evidence? Are Daubert-like criteria such as error rate and falsifiability more readily applied to evaluations of DNA evidence than other forms of evidence? Why or Why not?
Questions to consider when evaluating DNA evidence ... What kind of DNA test is at issue? How was the DNA extracted? How much DNA was extracted? How were the autoradiogram bands scored and sized? What were the match criteria and how were they applied? How was the DNA typed? What kind of tissue was being tested? (Blood, Semen, Other) Was the sample mixed with tissue (e.g., blood) from several possible sources? What kind of statistical estimates were made based on the match? What database was used for frequency statistics? Were there any allowances made for population structure? Were there estimates of error rates? Were there possible errors in collecting and/or contaminating samples? Have laboratory procedures used been reviewed? Are data available on laboratory error rates? Were there proper controls? What is the evidence being used for? Identification of a criminal suspect (Rape, Other) Identification of father in a paternity case Determination of lineage of plants or livestock for patent or trade secret purpose Other What are the background and qualifications of the expert? Expert from an academic institution Expert from commercial testing laboratory Expert from government crime laboratory Other How was the evidence presented? Were there invalid claims of uniqueness? Was there failure to consider genetic correlation among relatives? Were there invalid assertions regarding error rates? Were they any problems related to a mixed sample? From the Practitioner's Guide to the Federal Judicial Center's Reference Manual on Scientific Evidence, pg. 265.
Critical Questions Reviewed What kind of DNA test is at issue? What kind of tissue is being tested? Was the sample mixed with tissue from several possible sources? Was the crime scene contaminated? Was the sample too small for proper testing? Was there destruction of the sample? What about the problem of shifting bands? What about the possibility of false assumptions Were poor quality laboratory procedures used? Was the population database used too small or not appropriately used? What kind of statistical estimates were made based on the match? Were there estimates of error rates? What is the evidence being used for? What are the background and qualifications of the expert?
Endnotes: 1. "Introducing the Human Genome: The Recipe for Life" from To Know Ourselves: The U.S. Department of Energy and The Human Genome Project (July, 1996). 2. Significant articles and books relied upon for this chapter include: Wolfe, S.L. (1993). Molecular and Cellular Biology. Belmont, CA: Wadsworth Publishing Company; Kaye, D.H. and Sensabaugh, G. F. (1999). Reference Guide on Forensic DNA Evidence. Forthcoming, Federal Judicial Center; Federal Judicial Center (1994). Reference Manual on Scientific Evidence.; Thompson W. and Ford (1989). "DNA Typing: Acceptance and Weight of the New Genetic Identification Tests." Virginia Law Review, Vol. 75, pg. 45; Thompson, W. (1993). "Evaluating the Admissibility of New Genetic Identification Tests: Lessons From the 'DNA War." Journal of Criminal Law and Criminology, Vol. 84, pg. 22; Scheck, B. (1994). "DNA and Daubert." Cardozo Law Review, Vol. 15, pg. 1959; National Research Council Committee on DNA Forensic Science (1996). The Evaluation of Forensic DNA Evidence. Washington: National Academy Press. 3. This explanation of DNA and DNA testing is intended as an introduction to the subject for those who may have limited backgrounds in biological science. While accurate, this explanation involves somewhat of an over-simplification. Although intended to be informative, this is a brief and incomplete explanation of a complex subject. 4. Another category of repetitive non-coding DNA sequences is characterized by short core repeats (two to seven base pairs in length) and is known as 'short tandem repeats (STRs)'. 5. Commonwealth v. Lanigan, 596 N.E. 2d 311 (Mass. 1992). 6. NRC Report, Supra note 2, at 13. 7. NRC Report, Supra note 2, at 83 and 92. 8. Landar and Budowle. (1994). "DNA Fingerprinting Dispute Laid to Rest." Nature, Vol. 371, pg. 735. 9. This section is adapted from the Federal Judicial Center's Reference Manual on Scientific Evidence. (1994)
Glossary allele alternative form of a genetic locus (e.g., at a locus for eye color there might be alleles resulting in blue or brown eyes); alleles are inherited separately from each parent autoradiogram an x-ray film image showing the position of radioactive substances; sometimes called an "autorad" band shifting the phenomenon of DNA fragments in one lane of a gel migrating slower or faster than fragments in another lane; as visualized on an autoradiogram, the overall patterns would be the same, but out of register; factors responsible for band shift include contaminants, salt concentration, and DNA concentration base pair two complementary nucleotides (adenine and thymine or guanine and cytosine) held together by weak bonds; two strands of DNA are held together in the shape of a double helix by the bonds between base pairs chromosome a threadlike structure that carries genetic information arranged in a linear sequence; in humans, it consists of a complex of nucleic acids and proteins denaturing a process by which the hydrogen bonds on the original double-stranded DNA are broken, or 'unzipped,' leaving a single strand of DNA whose bases are available for hydrogen bonding DNA deoxyribonucleic acid; the molecule that encodes genetic information; double-stranded helix held together by weak bonds between base pairs of nucleotides DNA profile set of genotypes possessed by a person at two or more loci is a "multi-locus genotype" or "DNA profile" gel electrophoresis technique used to separate molecules such as DNA fragments or proteins; in forensic uses of DNA tests, electric current is passed through a gel, and the fragments of DNA are separated by size; smaller fragments will migrate farther than larger pieces gene the fundamental unit of heredity; an ordered sequence of nucleotide base pairs to which a specific product or function can be assigned genome all the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs genotype the genetic constitution of an organism hybridization the process of joining two complementary strands of DNA, or of DNA and RNA, together to form a double-stranded molecule locus a specific, physical position on a chromosome monomorphic locus on a DNA molecule where all humans have the same genetic code nucleotide the unit of DNA consisting of one of four bases - adenine, guanine, cytosine, or thymine - attached to a phosphate-sugar group PCR Polymerase Chain Reaction; a process through which repeated cycling of the reaction reproduces a specific region of DNA, yielding millions of copies from the original polymorphism the existence of more than one form of a genetic trait probe short segment of DNA that is labeled with a radioactive or other chemical tag and then used to detect the presence of a particular DNA sequence through hybridization to its complementary sequence restriction enzyme an enzyme normally found in bacteria which cuts DNA at specific sites (i.e., each time a specific nucleotide pattern occurs); because a restriction enzyme always acts upon DNA in the same manner, a map can be made of a restriction enzyme's actions on a known set of molecules southern blotting the transfer of molecules which have been separated by electrophoresis from the gel onto a membrane (named for the inventor) Variable Number Tandem Repeats repeated sequences of base pairs found in every strand of DNA; apparently do not supply any genetic information (VNTR)
Suggested Readings Bell, R. B. (1997). "Instructing Juries in Genomic Evidence Cases." Judges' Journal, Vol. 36(3). pg. 42. Coleman, H. and Swenson, E. (1994). DNA in the Courtroom, A Trial Watcher's Guide. Genelex Corporation. deral Judicial Center. (1994). Reference Manual on Scientific Evidence. Washington, D.C.: Government Printing Office. National Research Council. (1996). The Evaluation of Forensic DNA Evidence. Washington: National Academy Press. Inman, K. and Rudin, N. (1997). An Introduction to Forensic DNA Analysis. CRC Press. Kaye, D.H., and Sensabaugh, G.F. (1999). Reference Guide on Forensic DNA Evidence. Forthcoming, Federal Judicial Center. Lee, H.C., and Gaensslen, R.E. (1990). DNA and Other Polymorphisms in Forensic Science. Chicago: Year Book Medical. Scheck, B. (1994). "DNA and Daubert." Cardozo Law Review, Vol. 15, pg. 1959. Thompson, W.C. (1993). "Evaluating the Admissibility of New Genetic Identification Tests: Lessons from the 'DNA War.'" Journal of Criminal Law and Criminology, Vol. 84, pg. 22. Thompson and Ford. (1989). "DNA Typing: Acceptance and Weight of the New Genetic Identification Tests." Virginia Law Review, Vol. 75, pg. 45. Wolfe, S.L. (1993). Molecular and Cellular Biology. Belmont, CA: Wadsworth Publishing Company For more information on the Human Genome Project Human Genome Project Report, Part 1, Overview and Progress. (November, 1997). Human Genome Management Information System for the U.S. Department of Energy Research, Office of Biological and Environmental Research. Copies available upon request from the Human Genome Management Information System (HGMIS); Oak Ridge National Laboratory, 1060 Commerce Park, Oak Ridge, TN 37830. Electronic versions are accessible via the following websites: http://www.er.doe.gov/production/ober/HELSRD_top.html http://www.ornl.gov/hgmis/research.html To Know OURSEVLES: The U.S. Department of Energy and The Human Genome Project (July, 1996). Copies avilable from Human Genome News, Oak Ridge National Laboratory, 1060 Commerce Park, Oak Ridge, TN 37830. Information about the Human Genome Project can also be found at the following website: http://www.ornl.gov/hgmis
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