How are Restriction Enzymes Used in DNA Fingerprinting

Restriction enzymes are a type of endonucleases that can be used to cut double-stranded DNA at specific regions. They allow researchers to obtain desired DNA fragments from genomic DNA. In DNA fingerprinting, restriction enzymes can be used to cut DNA to obtain the banding pattern of STR.

Restriction enzymes are endonucleases that cut double-stranded DNA at the middle of the strand at specific sequences. They are used in a wide variety of genomic studies such as recombinant DNA technology, molecular cloning, restriction fragment polymorphism (RFLP) analysis, DNA mapping, etc. DNA fingerprinting is a technique in biotechnology used for the determination of the characteristics of DNA or the DNA profile of a particular organism. The DNA profile is generated based on a type of repeating elements known as short tandem repeats (STRs). During DNA fingerprinting, STR regions are digested with restriction enzymes to obtain a banding pattern called the DNA profile.

Key Areas Covered

1. What are Restriction Enzymes
– Definition, Features, Function
2. How are Restriction Enzymes Used in DNA Fingerprinting
– Role of Restriction Enzymes in DNA Fingerprinting

Key Terms: DNA Fingerprinting, Restriction Enzymes, Restriction Recognition Sites, Short Tandem Repeats (STRs)

What are Restriction Enzymes

Restriction enzymes are the endonucleases that cleave double-stranded DNA at specific DNA sequences known as restriction recognition sites. Hence, they are a type of biochemical scissors. Restriction enzymes are naturally produced by bacteria for the defense against bacteriophages. These enzymes are isolated from bacteria and are used to cut DNA in the laboratory. The ability of restriction enzymes to cut DNA at a precise location permits researchers to isolate desired DNA fragments from genomic DNA. The action of two restriction enzymes is shown in figure 1.

Figure 1: Restriction Enzymes

How are Restriction Enzymes Used in DNA Fingerprinting

In DNA fingerprinting, patterns of the repeating elements called short tandem repeats (STRs) are subjected to analysis. STRs are found in the centromeric regions of chromosomes, and they belong to the non-coding regions of the genome. Hence, STRs are a type of satellite DNA. Thus, shorts sequences of nucleotides (2-6 base pairs) are repeated a variable number of times in STRs. Since individuals have a different number of STRs at a given locus. Therefore, DNA profile is unique to a particular individual. In that sense, DNA fingerprinting can be used in the identification of individuals in paternity testing as well as in forensic investigations. The DNA fingerprinting technique was developed by Sir Alec Jeffreys in 1984. The procedure of DNA fingerprinting is described below.

DNA should be isolated from a given biological sample such as blood, saliva, semen, etc.
STR regions are amplified by PCR to obtain a considerable amount of DNA.
Amplified DNA can be subjected to digestion with restriction enzymes.
The fragments can be separated by gel electrophoresis based on their size.

Different banding patterns of STRs in several individuals are shown in figure 2.

How are Restriction Enzymes Used in DNA Fingerprinting

Figure 2: STR Patterns

Generally, human DNA consists of 700,000 restriction recognition sites throughout the genome. Therefore, a considerable number of restriction recognition sites can also be found within STR regions. By cutting STRs by restriction enzymes at a particular restriction recognition site, a banding pattern can be obtained. Due to the variable number of repeats in STR regions, the banding pattern also differs per individual.

Conclusion

Reference:

1. “DNA Fingerprinting.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 15 Feb. 2016, Available here.

Image Courtesy:

1. “TaiIMae” By Inks002 at the English language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “D1S80Demo” By PaleWhaleGail at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia