Chapter 19: Variable Number Tandem Repeat Profiling

The foundation of this approach rests on Restriction Fragment Length Polymorphism analysis, which begins by treating genomic DNA with restriction endonucleases that cleave the DNA molecule at specific recognition sequences, generating fragments of varying lengths. These fragments are then separated by size through gel electrophoresis, creating a pattern based on molecular weight distribution. The separated fragments are subsequently transferred onto a membrane using the Southern blotting technique, which enables targeted examination of specific DNA regions. The critical next step involves hybridization with complementary DNA probes that are either radioactively or chemically labeled, allowing visualization of specific VNTR loci. The chapter distinguishes between two primary probe strategies: the Multilocus Probe technique, which simultaneously detects multiple VNTR regions across the genome and generates complex banding patterns unique to individuals, and the Single-Locus Probe technique, which focuses on individual loci but offers improved specificity and easier interpretation. A significant portion of the chapter addresses the technical complexities inherent to these methods, including challenges posed by degraded or damaged DNA samples that may produce inconsistent fragment patterns, as well as various laboratory artifacts arising from improper restriction digestion, electrophoresis conditions, or membrane transfer procedures. The chapter also introduces Amplified Fragment Length Polymorphism analysis, a related approach incorporating polymerase chain reaction amplification with restriction digestion, representing an evolution toward more robust DNA characterization methods. Understanding these foundational techniques remains essential for comprehending modern DNA profiling methodologies and appreciating the historical development of forensic molecular biology.