Which type of genetic markers are commonly used in human DNA profiling for forensics?

• A. Mitochondrial DNA sequences only
• B. Short tandem repeats (STRs)
• C. Single nucleotide polymorphisms (SNPs) only
• D. Microsatellite deserts

Answer: (B)

Short tandem repeats are used in human DNA profiling because they are highly variable among individuals and can be readily amplified from small, even degraded, DNA samples. Each STR locus has a different number of repeated units, so the combination of multiple STR loci creates a highly distinctive genetic fingerprint for an individual. These markers are co-dominant, meaning both alleles at a locus are detected, which increases information content. The small size of STR amplicons makes them especially useful when crime-scene DNA is partial or degraded, and multiplex PCR allows many loci to be tested at once for efficient, reliable profiling. While mitochondrial DNA sequences are helpful in some forensic contexts, especially when nuclear DNA is unavailable, they are inherited maternally and offer less discrimination across unrelated individuals. SNPs can be informative, but typically require many more loci to achieve the same level of individual discrimination as STRs. “Microsatellite deserts” isn’t a recognized marker type in this context.