Why was it difficult to use dna as evidence in a crime before pcr was invented? a. you need many copies of dna for dna fingerprinting. b. pcr is the only way to cut dna into separate pieces. c. you need to be able to produce mrna from dna. d. it was impossible to copy dna before pcr was invented.

The correct answer is option A. "You need many copies of DNA for DNA fingerprinting".

Explanation:

Polymerase chain reaction (PCR) is a method that revolutionized molecular biology for its ability to create multiple copies of DNA at specific sequences. For instance, before PCR was invented it was difficult to use DNA as evidence in a crime because many copies of DNA are needed for DNA fingerprinting, the most widely used test to match the sample with the suspect. Nowadays, thanks to PCR, a drop of blood or a hair is enough to perform a DNA fingerprinting test.