Final answer:
PCR, or Polymerase Chain Reaction, is the technique that only needs a small sample of DNA for testing, as it can amplify specific segments of DNA from minimal starting material.
Step-by-step explanation:
The technique that only needs a small sample of DNA for testing is PCR (Polymerase Chain Reaction). PCR is a method used to amplify a specific segment of DNA, allowing us to start with a very small amount of DNA and generate enough material for testing and analysis. This technique utilizes an enzyme called DNA polymerase to rapidly replicate the DNA in a process that includes denaturation, annealing, and extension cycles.
Methods like SNP analysis, STR analysis, and cloning may also be performed using small amounts of DNA, but these are not exclusively known for requiring small samples. PCR stands out because it is specifically designed to amplify tiny amounts of DNA to make them large enough for further analysis, which is crucial when the initial sample is very limited.