Scientists typically amplify multiple str fragments from an individual in a single pcr. explain how they are able to do that.

STRs are short sequences of the DNA that are repeated multiple times on a DNA strand. The PCR process can multiply specific DNA sequences by using primers.
Primers are short DNA sequences that are complementary to the sequence we want to multiply. In the PCR (polymerase chain reaction) process primers can be used to amplify specific STRs. The PCR process has multiple cycles with temperature changes. In each cycle, the two DNA strands are separated and the primer and the STR are synthesized. With each new cycle, there is two times more of the amplified sequence, so the number of targeted sequences grows exponentially, resulting in a large number of copies of the sequence we want to have.

If there were no memes, there would be no life.