Case Study:

In modern forensic science, DNA fingerprinting has become an important tool for identifying individuals in criminal investigations and resolving family disputes. Every person’s DNA pattern is unique except in identical twins, because certain regions of DNA contain repeating sequences that vary among individuals. These repeating segments, known as Variable Number Tandem Repeats (VNTRs), help scientists create a unique DNA profile. 

In a district of Maharashtra, a jewellery shop robbery occurred. During the investigation, the police collected biological samples such as hair strands and a small blood stain from the crime scene. DNA was extracted from these samples and analyzed in a forensic laboratory. Scientists separated the DNA fragments using gel electrophoresis, which produced a pattern of bands called a DNA profile.

Three suspects-Ravi, Aman, and Imran-were questioned. DNA samples from the suspects were also collected and compared with the DNA profile obtained from the crime scene. The laboratory results showed that the banding pattern from the crime scene sample matched exactly with Ravi’s DNA profile but did not match with Aman or Imran.

DNA fingerprinting has been widely used in India for solving criminal cases and paternity disputes. Indian scientist Dr. Lalji Singh, often called the “Father of DNA Fingerprinting in India,” played a key role in introducing this technology for forensic investigations and court evidence. 

Based on the DNA comparison results, investigators concluded that Ravi was present at the crime scene. However, the final judgment still required careful legal evaluation of the evidence.

Questions:

Section A - MCQs

1. Why are DNA fingerprints unique for most individuals?
A. Because all humans have identical DNA sequences
B. Because some DNA regions contain repeating sequences that vary between individuals
C. Because DNA contains only four types of bases
D. Because DNA is present only in blood cells

2. If the DNA banding pattern from a crime scene exactly matches a suspect’s DNA profile, it suggests that:
A. The suspect definitely committed the crime
B. The suspect may have been present at the crime scene
C. The suspect and victim are identical twins
D. DNA fingerprinting is inaccurate

3. Which biological sample would be most useful for DNA fingerprinting in forensic investigations?
A. Sweat marks on walls
B. Hair with root attached
C. Dust particles
D. Ink stains

4. DNA fingerprinting cannot distinguish between:
A. Parents and children
B. Unrelated individuals
C. Identical twins
D. Brothers and sisters

Section B - Short Answer Questions

1. Explain why VNTR regions are useful in DNA fingerprinting. (2–3 marks)

2. How can DNA fingerprinting help resolve paternity disputes in courts? (2–3 marks)

3. In the case study, why is DNA evidence important but not the only factor in deciding the suspect’s guilt? (2–3 marks)

Section C – Long Answer Question

1. Suppose the DNA sample from the crime scene showed band patterns that partially matched two suspects instead of one.
Explain how scientists would further analyze the DNA evidence to identify the correct individual. Also discuss why multiple DNA markers improve the accuracy of DNA fingerprinting. (4–5 marks)

Answer Key:

MCQ Answers:

1. B
2. B
3. B
4. C

Section B Answers:

1. VNTR regions in DNA fingerprinting

• VNTRs are repeating DNA sequences found in certain regions of the genome.
• The number of repeats varies among individuals.
• This variation produces unique DNA banding patterns, helping identify individuals.

2. DNA fingerprinting in paternity disputes

• A child inherits half of its DNA from each parent.
• Scientists compare the child’s DNA bands with those of the mother and the alleged father.
• Matching bands confirm biological parentage.

3. Importance but limitation of DNA evidence

• DNA evidence strongly indicates whether a person was present at a location.
• However, contamination or secondary transfer is possible.
• Courts also consider other evidence such as witness statements and CCTV footage.

Section C Answer:

If DNA patterns partially match two suspects:

Step 1: Scientists analyze additional DNA markers (more VNTR or STR regions).
Step 2: Each marker produces another banding pattern.
Step 3: The suspect whose complete DNA profile matches the crime scene sample across multiple markers is identified.

Reason for multiple markers:

• Increases accuracy and reliability of identification.
• Reduces chances of coincidental matches.
• Ensures stronger scientific evidence in court.