What is an STR DNA profile and why is it central to modern forensic identification?

What is an STR DNA profile and why is it central to modern forensic identification?

• A. A profile based on mitochondrial DNA across a single locus; not useful for individual identification.
• B. A profile based on single nucleotide polymorphisms across the entire genome.
• C. A profile created to determine physical appearance.
• D. A profile based on Short Tandem Repeats across multiple loci; highly discriminative for individual identification.

Answer: (D)

Short tandem repeats (STRs) are short DNA sequences, typically 2–6 base pairs long, that occur in many locations across the genome. The key feature is that the number of times each repeat sequence is copied at a given locus varies greatly among individuals. A forensic STR profile is built by analyzing multiple such loci and recording the allele at each one—the combination of alleles across all loci creates a unique pattern for an individual. This multi-locus approach is what makes STR profiling so powerful for identification. Each locus contributes some variation, and when you gather data from many loci, the overall probability that two unrelated people share the exact same profile becomes astronomically small. That level of discriminative power is essential for confidently linking a DNA sample to a specific person or ruling out matches. STR profiling is also practical in forensic work because it works with small, sometimes degraded, samples and uses PCR to amplify the targeted loci. Laboratories standardize a set of core STR loci so results are comparable across cases and databases, further reinforcing its central role in modern identification. In contrast, mitochondrial DNA profiles rely on a single, maternally inherited region and are much less capable of distinguishing individuals, though they’re useful in certain scenarios (like degraded samples). While SNP-based approaches exist, STRs’ combination of high variability per locus and the ability to analyze many loci together makes them the backbone of routine forensic identification.

Short tandem repeats (STRs) are short DNA sequences, typically 2–6 base pairs long, that occur in many locations across the genome. The key feature is that the number of times each repeat sequence is copied at a given locus varies greatly among individuals. A forensic STR profile is built by analyzing multiple such loci and recording the allele at each one—the combination of alleles across all loci creates a unique pattern for an individual.

This multi-locus approach is what makes STR profiling so powerful for identification. Each locus contributes some variation, and when you gather data from many loci, the overall probability that two unrelated people share the exact same profile becomes astronomically small. That level of discriminative power is essential for confidently linking a DNA sample to a specific person or ruling out matches.

STR profiling is also practical in forensic work because it works with small, sometimes degraded, samples and uses PCR to amplify the targeted loci. Laboratories standardize a set of core STR loci so results are comparable across cases and databases, further reinforcing its central role in modern identification.

In contrast, mitochondrial DNA profiles rely on a single, maternally inherited region and are much less capable of distinguishing individuals, though they’re useful in certain scenarios (like degraded samples). While SNP-based approaches exist, STRs’ combination of high variability per locus and the ability to analyze many loci together makes them the backbone of routine forensic identification.