How is DNA profiling used in forensic science?

• A. By comparing DNA patterns, often using STRs amplified by PCR, to link a suspect to a crime scene.
• B. By sequencing the entire genome of suspects to determine ethnicity.
• C. By measuring protein levels in blood to identify individuals.
• D. By analyzing facial features to predict genetic traits.

Answer: (A)

DNA profiling relies on differences in short tandem repeats (STRs) at specific points in the genome. These regions vary in length between individuals, so each person has a unique pattern of STRs.

To create a DNA profile, scientists use PCR to amplify these STR regions from a small or degraded DNA sample. The resulting fragments are separated and sized, producing a pattern of STR lengths that acts like a fingerprint. Because most people have a unique combination of STR lengths (except identical twins), this pattern can be compared to samples from a crime scene or a suspect.

If the crime scene sample and the suspect’s sample share the same STR pattern, it strongly supports that they come from the same person, helping to link a suspect to the scene or to exclude someone from involvement. If they don’t match, the suspect is unlikely to be the source.

Other options don’t fit this use: sequencing the entire genome to determine ethnicity isn’t how forensic profiling is done and isn’t practical for identifying individuals; measuring protein levels isn’t a unique identifier; and predicting facial features from genetics isn’t a reliable or standard method for identifying a person.