OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

During genetic fingerprinting, what is used to separate DNA fragments?

1. Polymerase chain reaction

2. Gel electrophoresis

3. Photometric analysis

4. Fluorescent microscopy

The correct answer is: Gel electrophoresis

In genetic fingerprinting, gel electrophoresis is the technique used to separate DNA fragments based on their size. This process involves applying an electric current across a gel matrix, which causes the negatively charged DNA fragments to move toward the positive electrode. As they migrate through the gel, smaller fragments travel faster and further than larger ones, resulting in a separation of the DNA fragments according to their sizes. This separation allows scientists to create a distinct pattern of bands that can be visualized and analyzed, forming the basis for comparing different DNA samples. Such patterns are unique to individuals, making gel electrophoresis a critical step in processes such as paternity testing, forensic analysis, and in determining genetic relationships. Other methods listed, while useful in their respective contexts, do not serve the function of separating DNA fragments specifically during the fingerprinting process.