Solving Crime With DNA Analysis

Although the techniques that make it possible to identify a suspect using his genetic blueprint have been around since the mid-1980s, DNA analysis has increased in popularity in recent years. For one, TV shows such as "CSI: Crime Scene Investigation" has increased public awareness about forensics and DNA analysis through the use of cutting edge technology such as particle size analysers and DNA synthesizers that collect, determine and analyse DNA. So intriguing and convincing are the cases that today, many jurors expect to see DNA evidence in the courtroom.The truth of the matter is, DNA analysis is arguably the most important advancement in police work since fingerprint analysis. This breakthrough in genetic technology has not only brought present-day criminals to justice, it has also helped crack cases that have been unsolved for years.What is DNA?DNA stands for deoxyribonucleic acid and it the hereditary material in humans and almost all other organisms. Nearly every cell in a person's body has the same DNA and it contains information used everyday in metabolism and growth and it influences most of our characteristics.A DNA molecule is a long, twisting chain known as a double helix. In human cells, DNA is tightly wrapped into 23 chromosomes where one member of each chromosomal pair comes from your mother and the other from your father. To put it simply, your DNA is a combination of your mother and father's DNA and unless you have an identical twin, your DNA is unique to you.Collecting DNADNA can be collected from virtually anywhere. Even a criminal wearing gloves may unconsciously leave trace amounts of biological material such as hair, blood, semen, skin or even sweat. A few cells are all that are needed to obtain enough DNA information to identify a suspect.DNA Analysis Techniques 1. Restricted Fragment Length Polymorphism (RFLP) AnalysisOne of the first forensic methods used was RFLP analysis, which analyses the lengths of strands of DNA including repeating base pairs known as variable number tandem repeats. In this method, investigators need to dissolve DNA in an enzyme that breaks the strand at specific points. The number of repeats affects the length of each resulting strand of DNA and investigators compare samples by comparing the length of strands. RFLP analysis requires a large DNA sample that has not been contaminated with dirt.Today, many laboratories are replacing RFLP analysis with Short Tandem Repeat (STR) analysis, a method that offers several advantages, the biggest being its ability to start with a much smaller DNA sample.2. Y-marker AnalysisWhile most labs use either the RFLP or STR analysis methods, there are situations that require a different approach. For instance, in a situation such as a sexual assault case where there are multiple male contributors of genetic material, Y-marker analysis can resolve the mixture and sort out exactly which men were involved. This technique examines several genetic markers found on the Y chromosome. Since the Y chromosome is transmitted from the father to all his sons, the DNA on the Y chromosome can be used to identify the DNA from different males.3. Mitochondrial DNA (mtDNA) AnalysisRFLP and STR testing cannot be used on old remains or biological evidence lacking nucleated cells. In such situations, mtDNA analysis is used. This method uses DNA from a cell's mitochondria and has proven particularly useful in solving cold cases.4. Single Nucleotide Polymorphism (SNP) AnalysisSNP analysis is a fairly new technique and it is useful in cases where forensic labs are presented with highly degraded DNA samples. Scientists analyse variations in DNA where one nucleotide replaces another. This genetic change is called a single nucleotide polymorphism and it makes an excellent marker, one that can determine a person's susceptibility to certain diseases.Solving CrimesThere are two ways that DNA analysis can be performed to solve crimes. In cases where the perpetrator has been identified, DNA samples can be taken from the suspect and compared with DNA evidence found on the crime scene. If the samples match after being tested, the suspect can be charged.The second method is used when no suspect has been identified. With the help of equipment and techniques such as laser diffraction, DNA may be detected and collected from the crime scene. Under controlled circumstances, the sample DNA evidence is analysed and compared to DNA databases of offender profiles. A match can identify the perpetrator of the crime.