DNA fingerprinting is a technique used to determine the characteristics of DNA of a particular individual known as DNA profile. The DNA profile is unique to a particular individual. It is generated based on the short tandem repeats (STRs), types of repeating elements in the satellite DNA. As the DNA profile of a particular individual is unique, it can be used to identify individuals. Therefore, DNA fingerprinting is used in paternity testing and forensic investigations. In forensic testing, the amplifying power of PCR plays a critical role in recovering information from very small or degraded samples.
Key Areas Covered
1. What is DNA Fingerprinting
– Definition, Procedure, Role
2. Why Did the Invention of PCR Make DNA Fingerprinting Possible
– Use of PCR in DNA Fingerprinting
Key Terms: DNA Fingerprinting, DNA Profile, Forensic Investigations, Paternity Testing, PCR, Short Tandem Repeats (STRs)
What is DNA Fingerprinting
DNA fingerprinting is a technique used in the identification of individuals based on the unique patterns of their DNA. This technique was developed by Sir Alec Jeffreys in 1984. The patterns of the repeating elements called short tandem repeats (STRs) are subjected to the analysis. The STRs belong to the non-coding regions of the genome found in the centromeric regions. They are a type of satellite DNA. Shorts sequences of nucleotides (2-6 base pairs) are repeated a variable number of times in STRs. Since individuals have a different number of repeats at a given locus, the DNA profile is unique to a particular individual. The process of DNA fingerprinting is shown in figure 1.
Figure 1: DNA Fingerprinting
DNA Fingerprinting Procedure
- A DNA sample is isolated from a biological sample (blood, saliva, semen).
- The fragments are generated by digesting satellite DNA with restriction enzymes.
- The fragments are separated by gel electrophoresis.
Application of DNA Fingerprinting
DNA fingerprinting is used in both paternity testing and forensic investigations.
Paternity Testing
Since a child inherits half of the chromosomes from each parent, he has a combination of parental patterns of STRs. A paternity testing diagram is shown in figure 2.
Figure 2: Paternity Testing
When mother’s STR bands are subtracted from the child’s DNA profile, the remaining bands belong to #1 person. Therefore, he should be the biological father of the child.
Forensic Studies
DNA fingerprinting is also used in the forensic studies to identify the suspect by comparing the DNA profiles. However, the biological sample may be very small or degraded as it has to be collected from a crime scene.
Why Did the Invention of PCR Make DNA Fingerprinting Possible
The biological samples collected from a crime scene can either be very small or degraded. Therefore, the amount of satellite DNA may not be enough for detection in a gel. PCR is used to amplify the STR regions of the genome in order to obtain a considerable number of DNA for the restriction digestion. Hence, the use of PCR in DNA fingerprinting increases the discriminating power of the process.
Conclusion
DNA fingerprinting is the process of determining the DNA profile of an individual. The STRs are used to obtain the banding pattern known as DNA profile. The DNA profile is unique per individuals and therefore, it can be used in the identification of individuals in both paternity testing and forensic studies. However, small or degraded samples may produce poor discrimination between samples. Therefore, PCR can be used to amplify the STR regions to obtain high-intense banding patterns on a gel.
Reference:
1. Roewer, Lutz. “DNA Fingerprinting in Forensics: Past, Present, Future.” Investigative Genetics, BioMed Central, 2013, Available here.
Image Courtesy:
1. “Stages of Gene Fingerprinting” By Sneptunebear16 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “DNA paternity testing en” By Helixitta – Own work based on work File:Test na ojcostwo schemat.svg by Pisum (CC BY-SA 3.0) via Commons Wikimedia
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