Opinion ID: 1873955
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Heading: Theory and procedures involved in DNA print analysis.

Text: Many courts have stated that the general scientific theory underlying DNA print analysis is almost universally accepted in the scientific community. See, e.g., Caldwell v. State, 260 Ga. 278, 393 S.E.2d 436 (1990); People v. Castro, 144 Misc.2d 956, 545 N.Y.S.2d 985 (Sup.Ct.1989); State v. Schwartz, 447 N.W.2d 422 (Minn.1989); Andrews v. State, 533 So.2d 841 (Fla.Dist. Ct.App.1988). That underlying scientific theory was well explained in Castro, 144 Misc.2d at 961-63, 545 N.Y.S.2d at 988-89: DNA, deoxyribonucleic acid, is the fundamental natural material which determines the genetic characteristics of all life forms. Humans have human form and elephants have elephant form because of differences in the makeup of their respective DNA. Every cell that contains a nucleus contains DNA. There are approximately 10 trillion cells in the human body and most contain DNA. Red blood cells, which do not have nuclei, are a significant exception. Although the DNA is much too small to be seen by even the most powerful microscope, if it were stretched out to its full length, it would be about six feet long. Within humans, as a species, much of the DNA is identical. It is this identity of DNA that makes all humans look like humans, rather than dogs or trees. We humans create human offspring by transferring our DNA to our children. The science of genetics studies how and why this happens. DNA's fundamental structure, however, does not vary regardless of the type of genetic creature it creates. DNA is composed of a long double helix, which looks like a spiral staircase. The backbone of this molecule (i.e., the handrails and balustrade of the staircase) consists of repeated sequences of phosphate and deoxyribose sugar. Attached to the sugar links in the backbone are four types of organic bases: Adenine (A), Guanine (G), Cytosine (C) and Thymine (T). The steps of the staircase are formed by pairs of these bases (hereinafter, `base pairs'). A single DNA molecule consists of approximately three billion base pairs. Because of the chemical nature of the bases, only A and T can bond together, and only C and G can bond together. A cannot bond with G, and C cannot bond with T. Thus, the only possible combinations which can form the steps of the staircase are A-T, T-A, C-G, and G-C. The sequence of the three billion base pairs along the handrails of the DNA is the key to the information represented by the DNA. This sequence is responsible for producing arms, legs, kidneys or brain cells. Of this sequence, approximately 3 million sites vary from person to person. There are enormous differences between individuals because of the manner in which the base pairs are arranged. These variations, called polymorphisms or anonymous sequence, occur in different regions of the DNA. Polymorphisms are the basis of DNA identification. They are readily detectable when their lengths are altered by the action of restriction enzymes, thereby giving rise to `Restriction Fragment Length Polymorphisms' (hereinafter `RFLP'). The length of the fragment (or molecular weight) is measured by the distance it moves through an electrophoresis gel. Each individual's DNA is apportioned into forty-six discrete sections within the nucleus of each cell. These sections are called chromosomes. Twenty-two of these chromosomes come from the mother and twenty-two come from the father. These are genetically arranged in pairs. Additionally, two sex-typing chromosomes, denominated `X' and `Y' are present. During reproduction the chromosome pairs of the mother and the father split apart and then recombineone chromosome from the mother and one chromosome from the fatherto create the `new' twenty-two chromosome pairs of their child. Females have two `X' chromosomes, and males have one `X' and one `Y' chromosome, thus giving each human a total of forty-six chromosomes. A portion of DNA which is responsible for certain traits is called a gene (e.g., each person has a gene for the production of eyes). All humans have thousands of genes located on the forty-six chromosomes. Each gene is located at a specific site, or locus, upon a specific chromosome. Alternate forms of genes are called alleles (e.g., blue eyed allele, green eyed allele). This total pool of genetic information is known as the human genome. In chemical terms, the difference in alleles is explained by the difference in the ways the nucleotides, i.e. base pairs, arrange themselves along the DNA molecule. For example, one very short strand of DNA might look like: A T T C     T A A G while another might look like: A T A C     T A T G and a third might look like: C A A T     G T T A All are slightly different. Each is an allele. In actuality, however, each allele is much longer, i.e., on the order of 1,000-10,000 base pairs. Each base pair consists of a single nucleotide, that one bond between A and T or C and G. However, a very small variation in the order in which these base pairs occur on the DNA molecule can make huge differences. Sickle-cell anemia, for example, is caused by a single base pair on a single chromosome occurring out of order. If that single aberrant base pair were placed properly, the afflicted would not suffer from the disease. Obviously, if a DNA profile examined all three million sites of variation, each person's DNA could be individualized. Such an undertaking would be unduly burdensome in terms of time, labor, and cost. As an alternative to this approach, it is accepted that scientists can, in relative terms, discriminate between various people's DNA by examining several of these polymorphic sites. At a particular site or locus, a person may have a substantially unique pattern. For instance, a particular fragment size may occur in a small percentage of the population. By examining the sizes of a sufficient number of fragments at different sites on different chromosomes, statistical procedures permit enough discrimination to establish the unique configuration of any one persons's DNA pattern. Techniques for implementing DNA print analysis based on the theory above have also been discussed by other courts. In Schwartz, the Minnesota Supreme Court stated: Three commercial laboratories in the United States currently perform DNA analysis: Cellmark (the company that did the testing in this case) Lifecodes Corporation, and Cetus Corporation. Both Cellmark and Lifecodes employ restriction fragment length polymorphism (RFLP) analysis in their DNA testing. RFLP analysis involves the following steps: (1) Extraction: DNA is removed from the specimen and `washed' with an organic solvent. (2) Fragmentation: the extracted DNA chain is then cut into fragments at specific sites by mixing it with a restriction enzyme. (3) Gel electrophoresis: the DNA is placed in a gel to which an electrical current is applied, causing separation of the fragments into bands according to their length. (4) Southern [transfer]: the DNA bands are transferred to a nylon membrane while retaining the same positions they previously occupied on the gel. The double-stranded bands are then treated with a chemical that causes them to separate into single strands. (5) Hybridization: genetic probes (DNA clones) are applied, which bind to a specific, complementary DNA sequence on the membrane; the excess probe is then washed off. (6) Autoradiograph (or `autorads'): the membrane is exposed to an x-ray film and developed so that the DNA banding patterns and their lengths can be visualized. Finally, the autoradiograph is interpreted by comparing the DNA print to another DNA sample to determine if they match based on band length. 447 N.W.2d at 425. Schwartz's description of the procedures involved in the DNA print analysis technique employed by Lifecodes is consistent with Dr. McElfresh's description of the same techniques. The interpretation of the autorads is the basis for DNA matching evidence and DNA population frequency statistical evidence. Castro, 144 Misc.2d at 967, 545 N.Y.S.2d at 992, provides this explanation concerning interpretation of autorads: After the autorad has been produced the results must be interpreted. The bands on the autorad in different lanes must be examined to determine if they `match'. The bands in various lanes on the autorad are visually inspected to see if they co-migrate. If a match is declared, the issue is reduced to determining the likelihood that the match is unique. A match is said to occur if the sizes and number of the detected RFLPs in various lanes are indistinguishable within a permissible degree of error. They are then measured either manually or by a digitizer attached to a computer. Whatever standard of measuring error is used to determine if the bands are indistinguishable must also be used when calculating the frequency of the band in the population. The `uniqueness' question is answered according to the principles of population genetics, using the same matching rule or standard deviation. 144 Misc.2d at 967, 545 N.Y.S.2d at 992.