Types of DNA Analysis
DNA analysis is the process in which genetic sequences are studied. It is used by law enforcement and medical personnel to identify a particular person or species, and even specific cancers and diseases. At one point the analysis process was very limited. Now, DNA is analyzed using several processes.
There are Three Main Types of Forensic DNA Analysis
- Short Tandem Repeats (STR) using the Ploymerase Chain Reaction (PCR)
- Mitochondrial DNA (mtDNA)
The Y chromosome is very helpful in identifying suspects in forensic applications. The Y chromosome is only found in the males so that analyzing the male chromosome separates out the female DNA. This chromosome is only passed down from father to son, so it is also very useful in identifying familial relationships. An advantage to analyzing the Y chromosome is the ability to limit the potential pool of suspects, even when there is more than one male contributor found in a biological sample. With further advancements, the extraction process used to separate semen from vaginal cells before analysis may become unnecessary.
Short Tandem Repeat Analysis (STR)
Short Tandem Repeat (STR) analysis examines the specific areas (loci) on the normal or nuclear DNA. These regions of DNA are different for each person. Because of this, the testing process enhances the distinct differences between one DNA profile and another. With the exception of identical twins, there is an one in a 1,000,000,000,000,000,000,000,000,000 chance of two people sharing the same 15-loci profile.
CODIS uses a specified 13 STR loci as its standard, a standard that was chosen by the Federal Bureau of Investigation. Setting a standard guarantees that all forensic labs will be able to use the same DNA databases and have the ability to share forensic information. To use the CODIS database in unsolved cases, the profiles must be created using the STR process and the specified 13 loci that were determined by the FBI.
Mitochondrial DNA Analysis
Mitochondrial DNA (mtDNA) analysis is good for evidence that cannot be analyzed using traditional STR analysis. The mitochondrial DNA analysis technique uses DNA that is extracted from the mitochondrion. STR analysis uses DNA from the cell’s nucleus. Typically, mtDNA is used to extract DNA from old evidence like hair, teeth and bones that no longer has any nucleic DNA material to use for STR analysis. The mtDNA analysis process is extremely beneficial in helping to solve cold cases and unidentified remains.
Traditional STR analysis can be used to create a DNA profile from weakened evidence but materials like blood or semen may be too destroyed for PCR testing to generate an accurate profile. However, the hair shaft can be analyzed using mtDNA and can then play an important role in solving the case. Mitochondrial DNA is passed down to all of the offspring from only the mother, so all maternal relatives have the same mitochondrial DNA. Among other things this allows unidentifiable remains to be identified using the mtDNA of any maternal relative.
Polymerase Chain Reaction (PCR)
The Polymerase Chain Reaction is an important laboratory procedure used in STR or Short Tandem Repeat analysis. It is one of the most significant advances in science. The process involves copying a portion of DNA with a small molecular machine called polymerase, an enzyme, to duplicate DNA regions in a test tube. The process can be repeated to produce billions of DNA molecules in a few hours.
Unlike with other types of analysis, this DNA analysis process can reproduce DNA using a tiny sample of cells. Because this process requires only a small sample, a laboratory can analyze even the most degraded sample. The downside to polymerase chain reaction analysis is the contamination issue. This technique will replicate any DNA found in an evidence sample, requiring a greater amount of attention in the collection, identifying and preserving evidence. The contamination risk is important when investigating the evidence that may be stored or collected.