What is the basic principle of DNA collection from biological evidence?

• A. DNA must be collected only from blood.
• B. DNA collection should involve heating samples to 100 C.
• C. Collect and preserve DNA-containing materials (blood, saliva, sweat) using sterile tools, proper packaging, and chain of custody to ensure integrity.
• D. DNA is preserved by exposing to sunlight.

Answer: (C)

The basic principle is to collect and preserve DNA-containing materials in a way that keeps the genetic material intact and protects it from contamination. DNA isn’t found only in blood; it comes from many biological traces such as saliva, sweat, or other bodily materials, so the emphasis is on handling whatever material is available with care. Using sterile tools prevents introducing foreign DNA, proper packaging protects the sample from moisture, contamination, and physical damage, and maintaining a clear chain of custody documents every transfer and handling step to prove the evidence has not been altered. Heating samples to high temperatures would destroy DNA, and exposing them to sunlight can degrade the DNA and compromise the sample, so those practices undermine the goal of preserving genetic material for accurate analysis.