What is PCR and why is it used in forensic DNA analysis?

What is PCR and why is it used in forensic DNA analysis?

• A. Polymerase chain repair; it fixes damaged DNA before profiling.
• B. Polymerase chain termination; it's used to sequence DNA.
• C. Polymerase chain reaction; it amplifies small DNA quantities to produce enough material for STR profiling.
• D. Protein chain reaction; it amplifies proteins for identification.

Answer: (C)

PCR, or polymerase chain reaction, is a method that creates many copies of a specific DNA region. In forensic DNA analysis, this matters because crime-scene samples are often very small or degraded, so you need a lot of the exact DNA segments used for profiling. PCR uses primers that flank the short tandem repeat (STR) regions and a heat-stable DNA polymerase to copy the target DNA through many heating and cooling cycles. Each cycle doubles the amount of the target, so after enough cycles you have millions of copies. This amplification provides enough material for STR profiling, which determines the lengths of specific STR loci to generate a genetic fingerprint. After amplification, the products are analyzed (often by capillary electrophoresis) to read the allele sizes. The other statements don’t fit because PCR is not about repairing DNA, it’s about copying it; the term for terminating DNA synthesis to read sequences is polymerase chain termination, which is used in sequencing contexts rather than the standard STR amplification for forensic profiling; and a protein-focused term like protein chain reaction doesn’t describe a DNA amplification technique at all.

PCR, or polymerase chain reaction, is a method that creates many copies of a specific DNA region. In forensic DNA analysis, this matters because crime-scene samples are often very small or degraded, so you need a lot of the exact DNA segments used for profiling. PCR uses primers that flank the short tandem repeat (STR) regions and a heat-stable DNA polymerase to copy the target DNA through many heating and cooling cycles. Each cycle doubles the amount of the target, so after enough cycles you have millions of copies. This amplification provides enough material for STR profiling, which determines the lengths of specific STR loci to generate a genetic fingerprint. After amplification, the products are analyzed (often by capillary electrophoresis) to read the allele sizes.

The other statements don’t fit because PCR is not about repairing DNA, it’s about copying it; the term for terminating DNA synthesis to read sequences is polymerase chain termination, which is used in sequencing contexts rather than the standard STR amplification for forensic profiling; and a protein-focused term like protein chain reaction doesn’t describe a DNA amplification technique at all.