Why was it difficult to use DNA as evidence in a crime before the invention of PCR (polymerase chain reaction)?

• A. Because DNA could not be extracted from biological samples.
• B. Because there was not enough DNA in most samples to analyze accurately.
• C. Because DNA degraded instantly after being collected.
• D. Because DNA sequences were identical in all humans.

Answer: (B)

Verified step by step guidance

1. Understand the role of DNA in forensic science: DNA is a unique identifier for individuals (except identical twins) and can be used to link biological samples to specific people.
2. Recognize the challenge before PCR: In most crime scenes, the amount of DNA present in biological samples (like blood, saliva, or hair) is very small, making it difficult to analyze accurately.
3. Learn about PCR (Polymerase Chain Reaction): PCR is a technique that amplifies small amounts of DNA, creating millions of copies of a specific DNA sequence, which makes it easier to analyze even tiny samples.
4. Consider the limitations before PCR: Without the ability to amplify DNA, forensic scientists often faced issues with insufficient DNA quantities, leading to inconclusive or unreliable results.
5. Conclude why PCR was a game-changer: The invention of PCR allowed scientists to work with minimal DNA samples, overcoming the primary challenge of insufficient DNA for accurate analysis in forensic investigations.