35. Which of the following molecular genetic technique(s) is/are used in forensic science? 

(A) Coimmunoprecipitation

(B) DNA fingerprinting

(C) Restriction   fragment   length polymorphism

(D) Electrophoretic mobility shift assay

Which Molecular Genetic Techniques Are Used in Forensic Science?

Detailed Explanation

Forensic science uses biological and molecular techniques to examine evidence collected from crime scenes and establish links between biological samples and individuals. Among the techniques listed in the question, DNA fingerprinting and Restriction Fragment Length Polymorphism (RFLP) are used in forensic science because they can detect variations in DNA sequences among individuals.

The basic principle behind forensic DNA analysis is that, except for identical twins, individuals generally possess distinctive patterns at highly variable regions of their genomes. Biological materials such as blood, semen, saliva, hair roots, skin cells, and other tissues may contain DNA that can be analyzed to generate a genetic profile. This profile can then be compared with DNA obtained from a suspect, victim, relative, or reference sample.

DNA fingerprinting is directly associated with forensic identification, while RFLP is an important molecular technique that has historically been used to generate DNA profiles. Therefore, both option (B) and option (C) are correct.

Why Is DNA Fingerprinting Used in Forensic Science?

Option (B): DNA Fingerprinting — Correct

DNA fingerprinting, also called DNA profiling, is one of the most important molecular genetic techniques used in forensic science. It is based on the analysis of highly variable regions of the human genome that differ among individuals. These variations create characteristic DNA patterns that can be used for identification.

In forensic investigations, DNA may be isolated from biological evidence recovered from a crime scene. The resulting DNA profile is compared with a reference sample. A strong match between the profiles can provide powerful evidence that the biological material originated from the same individual.

DNA fingerprinting is used in criminal investigations, identification of unknown human remains, paternity and kinship analysis, disaster victim identification, and missing-person investigations. Its value comes from the high degree of variation found in selected regions of the genome.

Modern forensic laboratories commonly analyze Short Tandem Repeats (STRs). STRs are short DNA sequences repeated a variable number of times at particular genomic locations. Because the number of repeats varies among individuals, analysis of multiple STR loci produces a highly discriminating DNA profile.

Earlier DNA fingerprinting methods often focused on Variable Number Tandem Repeats (VNTRs) and used techniques such as RFLP and Southern blotting. Modern STR-based analysis is faster and can often work with smaller amounts of DNA, but the fundamental concept remains the same: genetic variation is used to distinguish one individual from another.

Therefore, DNA fingerprinting is a major forensic molecular genetic technique, making option (B) correct.

How Is RFLP Used in Forensic Science?

Option (C): Restriction Fragment Length Polymorphism — Correct

Restriction Fragment Length Polymorphism, commonly abbreviated as RFLP, is a molecular genetic technique used to detect differences in DNA fragment lengths among individuals. These differences may arise because of variations in DNA sequences that alter restriction enzyme recognition sites or change the distance between such sites.

In RFLP analysis, DNA is first extracted from the biological sample. The DNA is then cut using specific restriction endonucleases. These enzymes recognize particular nucleotide sequences and cleave DNA at or near those sites. Because individuals may differ in their DNA sequences, digestion can produce DNA fragments of different lengths.

The resulting DNA fragments are separated according to size by gel electrophoresis. They may then be transferred to a membrane by Southern blotting and detected using labeled DNA probes. The resulting banding pattern can reveal genetic differences between samples.

Historically, RFLP analysis played a major role in forensic DNA profiling, especially in the analysis of VNTR regions. If a crime-scene DNA sample produced a pattern corresponding to that of a reference sample, the result could support an association between the biological evidence and the individual.

However, classical RFLP analysis generally requires relatively large amounts of high-quality, non-degraded DNA. This limitation reduced its usefulness for highly degraded or very small forensic samples. Modern forensic laboratories therefore rely more heavily on PCR-based STR analysis. Nevertheless, RFLP remains an important forensic molecular genetic technique and is historically fundamental to the development of DNA profiling.

Therefore, option (C) is correct.

Why Is Coimmunoprecipitation Not the Correct Answer?

Option (A): Coimmunoprecipitation — Incorrect

Coimmunoprecipitation, commonly abbreviated as Co-IP, is primarily a biochemical and molecular biology technique used to study protein–protein interactions. It is not a standard technique for generating an individual’s DNA profile in forensic science.

In this method, an antibody is used to bind a specific target protein. If another protein is physically associated with the target protein, it may be pulled down together with the target. The interacting proteins can then be detected and analyzed, commonly by techniques such as Western blotting.

Coimmunoprecipitation is widely used in cell biology, molecular biology, cancer research, and signal transduction studies. Researchers use it to investigate whether two or more proteins are present in the same molecular complex.

The major distinction is that forensic DNA identification focuses on genetic variation in DNA, whereas coimmunoprecipitation focuses primarily on interactions between proteins. It does not produce a DNA fingerprint or an individual-specific genetic profile.

Therefore, option (A) is incorrect.

Why Is Electrophoretic Mobility Shift Assay Not the Correct Answer?

Option (D): Electrophoretic Mobility Shift Assay — Incorrect

The Electrophoretic Mobility Shift Assay, abbreviated as EMSA, is a molecular biology technique used mainly to study DNA–protein interactions or, in some cases, RNA–protein interactions. It is also known as a gel shift assay.

The principle of EMSA is based on the observation that a DNA fragment bound to a protein moves more slowly through a non-denaturing gel than the same DNA fragment in its free form. When a protein binds to a labeled DNA sequence, the resulting DNA–protein complex has reduced electrophoretic mobility and appears as a shifted band.

EMSA is commonly used to study transcription factors, DNA-binding proteins, regulatory sequences, promoters, enhancers, and other molecular mechanisms involved in gene regulation. For example, researchers may use EMSA to determine whether a transcription factor binds to a specific DNA sequence.

Although EMSA involves DNA and electrophoresis, it is not a standard method for identifying individuals from forensic biological samples. Its primary purpose is to investigate molecular interactions rather than analyze individual-specific DNA polymorphisms.

Therefore, option (D) is incorrect.

DNA Fingerprinting and RFLP in Forensic DNA Analysis

DNA fingerprinting and RFLP are closely related in the historical development of forensic genetics. DNA fingerprinting refers broadly to the generation of an individual-specific DNA profile, while RFLP is one of the molecular methods that has been used to detect DNA polymorphisms and generate such profiles.

In classical forensic DNA fingerprinting, DNA was digested with restriction enzymes, separated by gel electrophoresis, transferred to a membrane, and hybridized with probes that detected variable DNA regions. The differences in fragment lengths produced characteristic banding patterns. These patterns could then be compared between crime-scene evidence and reference samples.

This relationship explains why both options are correct. DNA fingerprinting is the forensic identification approach, whereas RFLP is a molecular technique that has been used in forensic DNA profiling.

Final Answer

The molecular genetic techniques used in forensic science among the given options are DNA fingerprinting and Restriction Fragment Length Polymorphism (RFLP).

Correct Option: (B) and (C)

DNA fingerprinting is used to generate individual-specific genetic profiles from biological evidence, while RFLP detects variations in DNA fragment lengths and has historically played an important role in forensic DNA analysis. Coimmunoprecipitation is mainly used to study protein–protein interactions, whereas EMSA is used to study DNA–protein interactions. Therefore, these two techniques are not standard methods for forensic DNA identification.