Microarrays are currently used by the medical research community to genotype DNA for thousands of single nucleotide polymorphisms (SNPs) to locate disease-causing mutations.04, 05 Research on these technologies is being conducted to determine forensic science applications.
Click here to read more about SNPs in Subject 09, Module 01.
Microarrays detect sequence variation. In the forensic community, microarrays allow for interrogation of a region of amplified DNA with known differences or hotspots. The GeneChip® technology offered by Affymetrix is a highly integrated functional robotic workstation, which uses the natural complementary interaction of DNA.06-08
The surface of the Affymetrix array is like a giant checkerboard. The array is a piece of coated quartz about the size of a thumbnail, which has over 400,000 squares known as features. The features are approximately five microns across and contain over a million copies of a unique probe. The probes are typically 25 bases in length. One probe from each pair perfectly matches its target DNA, while the other contains a single mismatch located in the middle of the 25-base probe sequence. This single mismatch acts as an internal control.09 The intensity of the internal control is measured to subtract out spurious signals and cross-hybridization.
Affymetrix has developed a human MitoChip for identification of mutations from disease-related specimens in the mtGenome. This is an array-based sequencing platform for rapid and high-throughput analysis of mtDNA in the coding region.10 Affymetrix is currently developing an mtDNA assay for use in the forensic community.
Nanogen Inc. has developed an electronic addressing assay to place DNA fragments at specific sites on a silicon microchip. The negatively charged DNA migrates toward areas of positive charge on the chip. Once the microchip has been addressed, then sample DNA is added and complementary DNA binds to the immobilized probes.11 Development is ongoing for forensic application.
< Previous Page :: Next Page >