Opinion ID: 1506658
Heading Depth: 1
Heading Rank: 34

Heading: Restriction Fragment Length Polymorphism (RFLP)

Text: At present, the most widely accepted DNA test is the RFLP analysis. See, e.g., Fishback v. People, 851 P. 2d 884, 892 (Colo. 1993) (holding that no serious dispute exists as to whether the techniques involved in RFLP analysis are generally accepted); State v. Moore, 268 Mont. 20, 885 P. 2d 457, 468 (1994) (concluding that the theory underlying DNA and RFLP technology is generally not open to serious attack and [] such evidence is widely admitted in various state and federal courts and jurisdictions); State v. Streich, 163 Vt. 331, 658 A. 2d 38, 48 (1995) (noting that we cannot find any recent decision under any standard of admissibility which refuses to admit the DNA match result based on the RFLP technology). Recently, in State v. Marcus, the Appellate Division recognized that the scientific community generally accepts RFLP analysis. 294 N.J. Super. 267, 683 A. 2d 221 (1996). As Judge Skillman stated, DNA testing by the RFLP method is generally accepted and is sufficiently reliable to warrant its admission in criminal cases. Id. at 285, 683 A. 2d 221. RFLP was not the DNA analysis employed in this case. A brief description of RFLP, however, may be useful as background information. RFLP focuses on non-functional regions of DNA known as variable-number tandem repeats (VNTRs). In these regions, which typically range from 500 to 10,000 pairs of nucleotides, a core sequence of approximately fifteen to thirty-five base pairs is repeated many times consecutively along the chromosome. The number of repeats varies among individuals. At a given locus or site on a chromosome, sequences with different numbers of repeated units are known as VNTR alleles. Because different VNTR alleles contain different numbers of repeats, these alleles can be identified by their lengths. National Research Council, The Evaluation of Forensic DNA Evidence 14-15 (1996) ( NRC Report ). In RFLP analysis, the recovered DNA sample and the sample from the suspect are treated with a restriction enzyme, which seeks out a specific nucleotide pattern on the DNA helixes. It then fragments the molecules at those sites. Because of VNTRs, the locations of these sites, and the lengths of the resulting fragments, differ among individuals. Through a process called gel electrophoresis the DNA fragments are sorted by size and split into single strands. These strands bond to a nylon membrane, where a specially treated and radioactively-tagged single strand of DNA, called a genetic probe, is applied. The genetic probe bonds with a targeted VNTR sequence. The nylon membrane is then placed in contact with a piece of X-ray film. The radioactivity of the probes exposes the film, producing a pattern of bands, like the bar-code on a box in a supermarket, where the probes have attached to VNTRs. This bar-code image is called an autoradiograph or autorad. Fragments from different donors contain different numbers of repeat units, with a corresponding variation in the lengths of the fragments. Typically, radioactive probes need days or even weeks to expose the film. Id. at 18. Generally speaking, RFLP testing is time-consuming and may require months for a complete analysis. Ibid. Comparison of the location of the bands reveals whether the targeted VNTR in the subject's DNA matches the DNA from the recovered genetic material. That analysis can lead with a high degree of certainty to a correlation between the DNA samples. The next step involves analysis of population statistics, which reveals the likelihood of a random match between the samples. Using single-locus probes, the probability of finding a random match between unrelated individuals on all bands of a DNA fingerprint is less than one in ten million. Using one multi-locus probe, the probability is about one in thirty-three billion. Thomas M. Fleming, Annotation, Admissibility of DNA Identification Evidence, 84 A.L.R. 4th 313, 324 (1991). One problem with RFLP testing is that it requires a large quantity of high-quality genetic material. For example, it requires at least a quarter-sized blood stain or a dime-sized semen stain. Unless those samples are recovered when relatively fresh, they will degrade into fragments too small for RFLP analysis. Id. at 320. Cellmark attempted RFLP testing in this case. The samples, however, were too degraded to permit RFLP analysis. Thus, Cellmark turned to a newer technology, which involved Polymerase Chain Reaction (PCR).