Opinion ID: 1673940
Heading Depth: 1
Heading Rank: 9

Heading: admission of forensic dna testing

Text: Since the discovery that genetic information is found in DNA (deoxyribonucleic acid) within the nuclei of cells, scientists have searched for a way to identify an individual by DNA testing. It is now scientifically recognized that there are tests which will identify a person based on an analysis of his DNA. See, e.g., State v. Pierce, 64 Ohio St.3d 490, 597 N.E.2d 107 (1992); Ex parte Perry v. State, 586 So.2d 242 (Ala. 1991); 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). All living cells which contain a nucleus also contain DNA. Within the DNA is the genetic pattern or code that gives each life form its characteristics. The fundamental structure of DNA is the same in all living things, but there are portions that vary from species to species, and, within a species, from individual to individual. Only identical twins have the same DNA patterns. This uniqueness is what gives DNA analysis its value. The DNA molecule is a remarkably stable structure, visualized as much like a twisted ladder or spiral staircase. The sides of the ladder are repeating phosphate and sugar sequences. The rungs of the ladder are formed by a pair of organic bases joined together. There are four organic bases found in DNA: adenine (A), guanine (G), thymine (T), and cytosine (C). Because the distance between the sides of the ladder is uniform, the bases can only bond together in certain ways. A and T can bond together, and G and C can bond together; therefore, the only base pairs that can exist are A-T, T-A, G-C, or C-G. Any other combinations would cause the sides of the ladder to be too far apart or too close together, and the DNA molecule would become unstable. Each side of the ladder contributes one of the organic bases in the base pair rungs. If the ladder was split down the middle, between the two bases in each rung, two complementary strands of DNA would result. That is, if one half of the ladder had a sequence of bases on its side that read A-G-A-C-T-G, then the complementary strand from the other half of the ladder would read T-C-T-G-A-C. Each molecule of DNA contains over three billion base pairs. The sequences of the base pairs in these billions are the genetic code that determines the makeup of each organism. In humans, several million of these sites vary from person to person, except in identical twins. These varying sequences are called polymorphisms or anonymous sequences, and their presence is the basis of one of the most widely-used methods of DNA identification, Restriction Fragment Length Polymorphism testing (RFLP, pronounced riflip). RFLP testing is based on the fact that the polymorphisms can be isolated from one person's DNA to yield a unique pattern, except from identical twins. The pattern produced by identical twins, though, would still be unique to those two individuals. DNA analysis has proven to be highly valuable in many areas  for example, in resolving cases of disputed paternity. Its inestimable value, however, lies in its potential to provide identification in criminal cases bordering on the absolute. [1] In the United States at the time of this trial, there were three commercial laboratories that performed DNA identification testing: Cetus, Lifecodes, and Cellmark, the latter the testing lab in this case. In addition, the FBI and some other law enforcement agencies had established their own DNA testing labs. Although there are different methods for analyzing DNA, Cellmark performs RFLP testing for forensic DNA analysis. The first step in RFLP testing is to obtain a sample of some substance that contains DNA. This could include white blood cells, hair cells, skin cells, or spermatazoa  any cell that contains a nucleus. Those cells are placed in a special solution that makes the nucleus release the DNA. Then the twisted ladder unwinds and becomes a straight ladder. Special enzymes, called restriction enzymes, are combined with the DNA ladder. Each particular restriction enzyme is specific in its action and will only cut the sides of the DNA ladder at a specific location. It is able to do this because it looks for a precise sequence of bases. Just as in this country we read in a standard manner, left to right, the base codes along one side of the DNA ladder must also be read in a standard direction. For instance, the restriction enzyme that recognizes the base sequence A-T-G-C-T-A, may cut that sequence between the G-C. Such an enzyme would, then, cut the DNA every time that it recognized the same sequence A-T-G-C-T-A along the sides of the DNA ladder. This would leave the side ladder in two shorter pieces: A-T-G and C-T-A. However, the same restriction enzyme would not cut the sequence A-T-C-G-T-A, because, reading left to right, the resulting fragments would be A-T-C and G-T-A. The enzymes are, therefore, very specific in their actions. The shorter pieces of DNA ladder are then separated by gel electrophoresis. This procedure involves loading each DNA sample into a separate well on a thin gel plate and then applying an electrical charge. Because the DNA has a negative charge, applying an electrical current to the gel plate will cause the DNA fragments to migrate through the gel, each sample in its own lane, much like the swimmers in a race. The heavier fragments of DNA, containing the most base pairs, will stop migrating first, and the shorter bands will migrate further. Thus, the fragments of DNA ladder will stop in a unique banding pattern, characteristic of each DNA sample. The DNA at this time is still in the double-stranded, ladder, form. The next step in RFLP testing is to treat the DNA to cut the base pair rungs to yield two single strands of DNA; this step may be likened to unzipping the DNA to give two single strands. The single-stranded DNA is then transferred onto a nylon membrane, with the bands from the gel staying in the same locations on the membrane that they occupied on the gel. The nylon sheet is then incubated with radioactive probes, each containing a segment of DNA with a specific, known sequence of bases. Each radioactively-labeled known sequence of DNA will find a fragment with its complementary sequence of bases and bind to it. The excess probe is then washed off the nylon membrane. After the excess probe has been removed, the membrane with the labeled DNA is exposed to a type of x-ray film. The resulting film, or autoradiograph (autorad), then shows a series of bands in each lane. Each lane contains a separate DNA sample, and the bands within each lane are unique to that sample. By comparing the banding patterns given by a sample of DNA from a known individual with the banding pattern from an unknown sample of DNA, it is possible to see if the patterns match. If the two samples do match, then the conclusion can be drawn that the known individual was in all likelihood the source of the DNA and a match. After determining that two samples do match, the question then arises of the statistical probability that the match is unique. Such a question arises because forensic DNA testing currently maps only some of the polymorphisms present in an individual. We need not discuss the question of admissibility of population statistics, however, because those statistics were ruled inadmissible by the trial judge. Polk requested that a hearing be held to determine the admissibility of the results of forensic DNA testing under the Frye test. Mississippi has continued to follow the Frye general acceptance standard even after the adoption of Rule 702 of the Mississippi Rules of Evidence. See Hardy v. Brantley, 471 So.2d 358, 366 (Miss. 1985); House v. State, 445 So.2d 815, 822 (Miss. 1984). Frye requires that the thing from which the deduction is made [be] sufficiently established to have gained general acceptance in the particular field in which it belongs. Frye v. United States, 293 F. 1013, 1014 (D.C. Cir.1923). While Polk does not expressly urge this Court to abandon the Frye standard and adopt the test from People v. Castro, 144 Misc.2d 956, 545 N.Y.S.2d 985 (Sup.Ct. 1989), for determining the admissibility of forensic DNA analysis, Polk does make numerous references to the Castro test. After a careful review of the record, as well as the available information from other jurisdictions regarding forensic DNA testing, this Court adopts the modified version of the Castro test set forth by the Supreme Court of Alabama in Ex parte Perry v. State : I. Is there a theory, generally accepted in the scientific community, that supports the conclusion that DNA forensic testing can produce reliable results? II. Are there current techniques that are capable of producing reliable results in DNA identification and that are generally accepted in the scientific community? III. In this particular case, did the testing laboratory perform generally accepted scientific techniques without error in the performance or interpretation of the tests? Ex parte Perry v. State , 586 So.2d 242, 250 (Ala. 1991). [2] We therefore will examine the evidence using the three-pronged test from Perry.