Question

In this assignment, you will write about the applications of DNA technology in forensics, medicine, and agriculture.

Describe two different methods that can be used to assist in solving crimes and missing-person cases. Explain the benefits of each.

Answer 1

Here are two widely used DNA-based methods that help solve crimes and locate missing persons, with how they work and the main benefits of each.

1) Short Tandem Repeat (STR) profiling (DNA fingerprinting)
- What it is / how it works:
- STRs are short repeating DNA sequences at specific loci in the nuclear genome. Forensic labs amplify a standardized panel of STR loci by PCR and separate the fragments by size (capillary electrophoresis) to produce a profile.
- The profile is compared to known samples or to forensic databases (e.g., CODIS in the U.S.).
- Benefits:
- Very high discriminatory power — combinations of many STR loci give extremely low probabilities of two unrelated people matching, so it can strongly link a suspect to biological evidence or exclude persons of interest.
- Standardized and validated across forensic labs, enabling reliable comparisons and database searching (matching evidence to previous offenders or linking multiple crime scenes).
- Works on a wide range of sample types (blood, semen, saliva, hair with root, skin cells) and is relatively fast and cost-effective.
- Useful for identifying remains when a reference sample from a known individual (personal item or family member) is available for direct comparison.

2) Forensic genetic genealogy (FGG) / SNP-based genealogy
- What it is / how it works:
- Instead of STRs, FGG uses dense single nucleotide polymorphism (SNP) profiles (like those from consumer DNA tests). Investigators create a SNP profile from crime-scene DNA or remains, upload it (where permitted) to public or law-enforcement-accessible genealogy databases, and identify genetic matches (distant relatives).
- Genetic matches are combined with traditional genealogical research (family trees, public records) to narrow down potential identities and generate investigative leads.
- Benefits:
- Can identify suspects or missing persons even when no direct profile exists in criminal databases — especially powerful for cold cases and unidentified remains where STR database searches fail.
- Effective at finding distant relatives (second–fourth cousins), enabling reconstruction of family lines and pointing to probable identities when STR matching is impossible.
- Has solved numerous cold cases and helped identify long-unidentified human remains (high impact in both criminal investigations and missing-person recovery).
- Can work with degraded samples if SNP data of sufficient quality can be obtained (often via targeted sequencing).

Brief note on complementary use
- These methods are often complementary: STR profiling remains the standard for court-admissible identification and database comparisons, while FGG is a powerful investigative tool to generate leads when STR searches return no match. Both have helped close crimes and bring closure in missing-person and unidentified-remains cases.