How is a DNA fingerprint made in the lab?

In one line

The rule

DNA fingerprinting is a laboratory technique that identifies individuals by analyzing unique patterns in their DNA.

No single formula, but the process involves: extracting DNA, cutting it with enzymes, separating pieces by size, and visualizing the pattern.

Let's understand it simply

Imagine you have a long string of beads (DNA) with colored beads in a special order. Every person’s string has a slightly different pattern. If you cut these strings at certain colors and then sort the pieces by size, you get a unique set of bands for each person. This set of bands is your DNA fingerprint.

Think of it like rolling out a long roll of dough (your DNA) and using cookie cutters (enzymes) to cut it into pieces. When you line up the cookies by size, the pattern is different for everyone.

How it works

1. Collect a sample: Take cells from blood, hair, or saliva. These have DNA inside.
2. Extract the DNA: Break open the cells and pull out the DNA using chemicals.
3. Cut the DNA: Use special proteins called restriction enzymes (like scissors) to cut the DNA at certain spots.
4. Separate the pieces: Place the cut DNA on a gel (like jelly) and run electricity through it (gel electrophoresis). Smaller pieces move faster, so they travel farther.
5. Transfer and visualize: Move the DNA from the gel onto a nylon sheet. Add a probe (a piece of DNA with a marker) that sticks to certain DNA parts. This makes the bands visible.
6. Compare the pattern: The bands make a pattern, like a barcode. Compare this pattern to others to see if they match.

The story behind it

DNA fingerprinting was developed by Sir Alec Jeffreys in 1984 in England. He was studying how DNA varies between people. One day, he noticed that certain DNA patterns were unique to each person (except identical twins). This discovery helped solve crimes and identify people.

A famous early use was in a murder case in the UK, where DNA fingerprinting proved a suspect innocent and caught the real criminal. Jeffreys’ lab became famous for this new way to identify people.

Where you see it in real life

• Crime scenes: Police use DNA fingerprints to match suspects to blood or hair found at the scene.
• Paternity tests: To check if a man is the biological father of a child.
• Disaster victim identification: After accidents, DNA helps identify bodies when faces are unrecognizable.
• Wildlife conservation: Scientists track animals and catch poachers by matching DNA from fur or droppings.
• Missing person cases: DNA from relatives can help find missing children.
• Immigration cases: To prove family relationships when documents are missing.

Why it matters

• Solves crimes: Helps police catch the right person and free the innocent.
• Family and inheritance: Proves relationships in court.
• Medical research: Finds genetic diseases and helps in organ transplants.
• Wildlife protection: Tracks endangered animals and stops illegal trade.

Worked example

Let’s say police find a blood stain at a crime scene. Here’s how they make a DNA fingerprint:

Given: Blood sample from crime scene, and suspects’ blood samples.
Step 1: Extract DNA from all samples.
Step 2: Cut DNA with restriction enzymes.
Step 3: Run all samples on a gel with electricity (gel electrophoresis).
Step 4: Transfer DNA bands to a nylon sheet.
Step 5: Add a probe to make bands visible.
Step 6: Compare the band patterns from the crime scene to the suspects.
Step 7: If a suspect’s pattern matches the crime scene, they were likely present.

Common mistakes

• Thinking DNA fingerprint is a real fingerprint: It’s not a finger mark, but a pattern of DNA bands.
• Believing everyone’s DNA fingerprint is the same: Only identical twins have the same pattern; everyone else is unique.
• Assuming the whole DNA is used: Only certain parts (that vary a lot) are used for fingerprinting.
• Mixing up DNA fingerprinting with blood group tests: Blood groups are not unique, but DNA fingerprints are.

Remember it

DNA fingerprinting is like making a barcode from your DNA—unique for each person (except identical twins).