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DNA Testing: How It Works From Sample to Results

From Mouth Swab to DNA Fingerprint

Have you ever wondered how a simple cheek swab can reveal so much about you? It all boils down to DNA, the instruction manual that makes you, you. Here’s how our laboratory technicians crack the code from a mouth swab to create a unique DNA profile:

1. Sample Collection:

The journey starts with collecting cells from the inside of your cheek. These cells contain the DNA blueprint. A long handled cotton swab, called a buccal swab, is used for this painless process. It is very important that the top of this swab only comes into contact with the inside of the mouth, never any other object.

The buccal cells are then sent to our laboratory to begin the process. Once all samples have arrived, they are logged in and we make certain that the case number on the samples match the names on our order form.

2. Cell Lysis:

Imagine the cells as tiny safes holding the DNA. The lab uses a special solution with enzymes that act like keys. These enzymes break open the cell walls, releasing the DNA from its safe.

The solution used for the cells to be lysed (broken open) using a lysis buffer containing:

  • Detergents (e.g., Sodium Dodecyl Sulfate – SDS) to dissolve cell membranes.
  • Proteases (e.g., Proteinase K) to degrade proteins within the cell.
  • Chelating agents (e.g., EDTA) to inactivate nucleases (enzymes that degrade DNA).

Think of DNA as long, thin strands. Now that the “safes” are open, the DNA is floating around with other cell stuff. Technicians use chemicals that act like magnets, specifically attracting the DNA strands. This separates the DNA from the rest of the cellular clutter.

3. DNA Purification:

After getting the DNA, it is necessary to wash away the leftover cell parts and the chemicals they used. This leaves behind a purified sample of DNA, like a single strand of spaghetti after cleaning the kitchen.

Several methods can be employed to purify DNA:

  • Phenol-Chloroform Extraction: This traditional method utilizes the immiscibility of organic solvents (phenol and chloroform) with water. DNA partitions into the aqueous phase, while cellular debris remains in the organic phase.
  • Column Chromatography: Lysate is passed through a silica-based column. Buffers with varying ionic strengths selectively bind and elute cellular components, leaving purified DNA behind.
  • Magnetic Bead-Based Extraction: Magnetic beads coated with specific DNA binding moieties capture DNA from the lysate. The beads are then separated magnetically, allowing for efficient DNA isolation.

4. Duplication of the DNA (Photocopying the Code):

DNA is tiny, so it is necessary to make millions of copies using a machine called a thermal cycler. Imagine a high-tech photocopier specifically for DNA! This allows them to work with the DNA more easily.

The amount of extracted DNA is the quantified using a process called spectrophotometry (measuring UV absorbance) or fluorometry (measuring fluorescent dye binding to DNA).

5. Building Your DNA Profile (Fingerprint):

Each person’s DNA is unique, like a personal barcode. We use a technique called gel electrophoresis to separate the DNA copies by size. The quality of the DNA is then assessed by gel electrophoresis. Visualization of intact high-molecular weight DNA bands ensures suitability for downstream analysis. Picture separating different colored beads by size. This creates a unique pattern of bands, like a fingerprint for your DNA, called a DNA profile.

So, from a simple mouth swab, scientists can extract your DNA, make copies, and create a unique DNA profile that acts like a personal identification code!

6. Interpretation and Applications:

DNA profiles can be compared to known reference samples (another person’s DNA profile) or databases for identification purposes.

We then use statistical analysis to provide the probability of a random match between two profiles.

The applications we use this information for is in paternity testing and determining biological relationships. We can also use it for forensic investigations by linking crime scene evidence to suspects. This is also how ancestry analysis which is tracing genetic heritage is done.

Important to Remember:

  • This is a simplified explanation. DNA extraction is a more complex process in a lab setting.
  • DNA profiling is a powerful tool used for many purposes, and we are committed to use it ethically and with proper legal procedures.
  • Contamination prevention is crucial throughout the process to maintain sample integrity.
  • DNA yield and quality can be affected by factors like storage conditions and individual variability.
  • Ethical considerations and legal frameworks govern the use of DNA profiling in various contexts.