Opinion ID: 883138
Heading Depth: 1
Heading Rank: 6

Heading: PCR Analysis

Text: AGTC tested the brain tissue by conducting polymerase chain reaction testing. The following discussion of PCR testing is taken from Thomas M. Fleming, Annotation, Admissibility of DNA Identification Evidence, 84 A.L.R.4th 313 (1991), and testimony from the trial, unless otherwise noted. PCR testing is used to increase the amount of the DNA sample. This technique makes DNA testing possible on much smaller samples than RFLP analysis. However, PCR's ability to identify a particular individual to the exclusion of others is much lower. In this procedure, DNA is extracted from a sample purified and added to a buffer solution containing chemical primers and an enzyme called TAQ polymerase. The solution is then placed in a heating device, called a thermal cycler, which cycles it through several successive temperature plateaus. After 30 or 40 of these cycles, the DNA has become denatured. The primers have annealed to the DNA, identifying a gene of interest, in this case the DQ-alpha gene, which will have been replicated or amplified by the enzyme billions of times. Next, the amplified DNA is flooded over a nylon membrane onto which have been dotted a number of allele-specific probes, each designed to recognize one variant of the DQ-alpha gene. This will result in a color reaction and a visible dot on the membrane wherever a probe has identified one of the alleles. This genetic marker system has six traits which are simply numbered, 1.1, 1.2, 1.3, 2, 3, and 4. These alleles are combined in pairs in each person, because one is received from each parent. There are 21 possible pairs of these traits, and each pairing is called a genotype. The purpose of the testing is to identify the genotype present in the amplified DNA. After conducting PCR analysis on the piece of brain tissue, AGTC typed it as a DQ-alpha 3, 4. AGTC also conducted PCR analysis on the Brisbin family members and found that ... among [the] four children, there are only two alleles found, the 4 allele ... and a 3 allele. Since any given person can only have two alleles, the biological father of these individuals has to have a 3 allele and a 4 allele. The evidentiary material, the brain tissue, typed as a 3, 4 so it cannot be excluded as having come from the biological father. In sum, the PCR process clones the region of a DNA strand containing the DQ-alpha gene. The copies are then analyzed to determine whether certain sequences of the gene are present.