DNA profiling fundamentals: STRs and mixtures

What you’ll learn and practice

Work through the essentials of STR-based DNA profiling, including allele naming, genotype patterns, and how profiles are compared in casework.

Mixture interpretation is a major focus too—expect scenarios that test contributor count, major/minor components, and when a profile is not suitable for comparison.

Quiz format and difficulty settings

Each question has 4 options and there’s no timer, so you can slow down and reason through electropherogram-style logic and terminology.

Choose your question count before starting, and select an easier or harder mix depending on whether you want quick revision or deeper challenge; the overall difficulty is balanced by blending straightforward definitions with applied interpretation.

Common pitfalls to avoid

• Confusing allele count with contributor count in mixed samples
• Treating stutter, drop-in, or drop-out as definitive alleles without context
• Forgetting that homozygotes can look like “missing” alleles at a locus
• Over-interpreting low-level peaks or partial profiles beyond what they support
• Mixing up match statements, exclusions, and “inconclusive” outcomes

Tips to improve your score

Aim to justify each choice with a simple rule (e.g., peak patterns per locus, major/minor logic, or artifact awareness) rather than guessing from buzzwords.

If you miss a question, revisit what assumption failed—most errors come from skipping a constraint like peak height balance, locus-by-locus reasoning, or the limits of partial data.