100+ Free ABC Forensic DNA Practice Questions

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An analytical threshold (AT) and a stochastic threshold (ST) in STR interpretation primarily address which two issues, respectively?

Inhibition and degradation

Stutter and pull-up

Background signal/noise and allelic drop-out risk at low template

Sample mixing and PCR contamination

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Key Facts: ABC Forensic DNA Exam

CODIS core STR loci (since January 1, 2017)

FBI Laboratory CODIS Unit

75 + 15

Scored + pilot questions on ABC-DNA

ABC Forensic DNA page (criminalistics.com)

2 hr 15 min

Maximum test time for ABC-DNA

ABC Forensic DNA page

$325

Application + examination sitting fee

ABC Fees page

5 years

Certification cycle before recertification

ABC Recertification page

Y-STR loci amplified by Yfiler Plus

Thermo Fisher Yfiler Plus product literature

~6.6 pg

DNA per diploid human cell nucleus

Butler, Forensic DNA Typing (3rd ed.)

External proficiency tests per analyst per calendar year

FBI QAS for Forensic DNA Casework Laboratories

ABC's Forensic DNA exam contains 75 scored questions plus 15 pilot questions, delivered in 2 hours 15 minutes at an in-person ABC-approved test location. Fees are $75 application and $250 examination sitting; the certificate is valid for 5 years with a $100 annual recertification maintenance fee. Eligibility requires active employment in a forensic DNA lab and meeting the FBI QAS education, training, and experience standards. Topics span autosomal STR typing (20 CODIS core loci), Y-STR (Yfiler Plus 27 loci), mtDNA HV1/HV2 sequencing, mixture interpretation, probabilistic genotyping (STRmix, TrueAllele, EuroForMix), CODIS/NDIS rules, FBI QAS, ISO 17025, OSAC standards, and emerging methods such as MPS and Investigative Genetic Genealogy.

Sample ABC Forensic DNA Practice Questions

Try these sample questions to test your ABC Forensic DNA exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1DNA is described as a double helix. Which pair correctly represents the complementary base pairing in double-stranded DNA?

A.Adenine pairs with thymine; cytosine pairs with guanine

B.Adenine pairs with cytosine; thymine pairs with guanine

C.Adenine pairs with uracil; cytosine pairs with guanine

D.Adenine pairs with guanine; cytosine pairs with thymine

Explanation: Watson-Crick base pairing in DNA is A-T (two hydrogen bonds) and C-G (three hydrogen bonds). Uracil replaces thymine only in RNA, not DNA. These pairings underpin all PCR primer design and capillary electrophoresis (CE) detection in forensic STR analysis.

2Which of the following statements about nuclear DNA versus mitochondrial DNA is correct for forensic biology?

A.Nuclear DNA is inherited only from the father; mtDNA is inherited from both parents

B.Nuclear DNA is biparental and unique per individual; mtDNA is maternally inherited and shared among maternal relatives

C.Both nuclear DNA and mtDNA are inherited only from the mother

D.mtDNA is unique per individual; nuclear DNA is shared among siblings

Explanation: Nuclear DNA is biparental (half from each parent) and, except for identical twins, unique to the individual. Mitochondrial DNA is inherited only from the mother, so all maternal relatives share the same mtDNA haplotype, which limits its discrimination power but enables identification when nuclear DNA is degraded.

3How many CODIS core STR loci are required for upload to the U.S. National DNA Index System (NDIS) following the January 1, 2017 expansion?

A.13 core loci

B.16 core loci

C.20 core loci

D.24 core loci

Explanation: On January 1, 2017, the FBI expanded the CODIS core loci from 13 to 20 autosomal STRs to increase discrimination power and support international data sharing. The added loci include D1S1656, D2S441, D10S1248, D12S391, D22S1045, D2S1338, and D19S433. Amelogenin remains the standard sex-typing marker.

4Which STR locus is on the X chromosome and the Y chromosome and is used as a sex-typing marker in forensic STR kits?

A.D8S1179

B.Amelogenin

C.FGA

D.vWA

Explanation: Amelogenin produces a single peak at ~106 bp (X) in females and two peaks (X at 106 bp; Y at 112 bp) in males. It is included in essentially every modern forensic STR kit (GlobalFiler, PowerPlex Fusion 6C, Investigator 24plex). Y-deleted males can give false-female amelogenin results, so Y-STR confirmation is sometimes required.

5An analyst uses Chelex 100 for DNA extraction. Which statement best describes the mechanism and the resulting DNA?

A.Chelex chelates magnesium ions and denatures cellular proteins, yielding single-stranded DNA suitable for PCR

B.Chelex precipitates DNA in ethanol, yielding purified double-stranded DNA

C.Chelex binds DNA to magnetic beads, yielding column-purified DNA

D.Chelex digests proteins via proteinase K only, yielding RNA-rich extract

Explanation: Chelex 100 is a chelating ion-exchange resin that binds polyvalent metal cations (notably Mg2+), inactivating nucleases. Heating in Chelex lyses cells and denatures the DNA, so the resulting extract contains single-stranded DNA. The method is quick and inexpensive but does not purify the extract, so PCR inhibitors can carry through.

6Which extraction method historically yields the highest-purity, double-stranded DNA but uses hazardous solvents?

A.Chelex 100

B.DNA IQ magnetic-bead system

C.Organic phenol-chloroform extraction

D.FTA paper direct amplification

Explanation: Phenol-chloroform-isoamyl extraction followed by ethanol precipitation produces high-quality double-stranded DNA suitable for downstream techniques such as mtDNA sequencing. Drawbacks are hazardous waste handling, multiple tube transfers (contamination risk), and longer hands-on time, which is why many labs replaced it with magnetic-bead chemistries.

7What is the purpose of an internal positive control (IPC) in real-time PCR quantitation kits such as Quantifiler Trio?

A.It quantifies the target human DNA

B.It detects PCR inhibition independent of the target by amplifying a known synthetic sequence

C.It corrects for stutter products in STR amplification

D.It calibrates the analytical threshold on the CE instrument

Explanation: The IPC is a synthetic template spiked into every reaction at a known concentration. A delayed or absent IPC Ct signal with negative or low human-DNA signal indicates PCR inhibition (e.g., humic acid, hematin, indigo) rather than absence of human DNA. Quantifiler Trio also reports autosomal, Y, and degradation-index targets.

8The Quantifiler Trio degradation index (DI) is calculated by which ratio?

A.Small autosomal target / large autosomal target Ct difference, expressed as a ratio of quantities

B.Y-target quantity / autosomal-target quantity

C.IPC Ct / autosomal Ct

D.Stutter ratio / parent peak ratio

Explanation: Quantifiler Trio amplifies a short (~80 bp) and a long (~214 bp) autosomal target. DI = (small-target ng/uL) / (large-target ng/uL). A DI near 1 indicates intact DNA; a DI substantially greater than 1 (commonly >10) indicates progressive degradation, signaling that the larger STR amplicons may drop out.

9Which thermocycler step in PCR allows the primer to bind specifically to its complementary sequence on the template DNA?

A.Denaturation, typically 94-96 C

B.Annealing, typically 50-65 C

C.Extension, typically 72 C

D.Final hold, typically 4-15 C

Explanation: PCR uses three thermal phases per cycle. Denaturation (~95 C) separates the strands; annealing (~55-60 C for most forensic STR kits) lets primers hybridize to complementary sequence; extension (~72 C) allows Taq polymerase to synthesize new strand. Lower annealing temperatures can produce non-specific products; higher temperatures can cause primer drop-out.

10STR stutter peaks most commonly appear at what position relative to the true allele, and at what typical magnitude?

A.One repeat unit larger; usually less than 5% of the parent peak

B.One repeat unit smaller; typically less than 15% of the parent peak

C.Two repeat units smaller; typically less than 30% of the parent peak

D.One repeat unit smaller; typically equal to the parent peak

Explanation: Stutter arises from polymerase slippage during PCR. The dominant n-4 (one repeat shorter) stutter typically runs <15% for tetranucleotide STRs, with locus-specific thresholds in kit validation. Forward (n+4) and double-back (n-8) stutter are much less frequent and have lower thresholds.

About the ABC Forensic DNA Exam

The ABC Forensic DNA specialty exam (ABC-DNA, sometimes referred to as Molecular Biology / ABC-MB in legacy materials) certifies forensic DNA analysts in casework or databasing roles. It is an in-person, proctored exam administered by the American Board of Criminalistics and is one of ABC's five active specialty examinations alongside Biological Evidence Screening, Drug Analysis, Foundational Knowledge, and Seized Drug Analysis.

Questions

90 scored questions

Time Limit

2 hours 15 minutes

Passing Score

Cut score set by ABC during exam development; numeric value not disclosed to candidates

Exam Fee

$75 application + $250 examination sitting + $100 annual recertification maintenance (American Board of Criminalistics (ABC))

ABC Forensic DNA Exam Content Outline

Foundational

Molecular Biology Foundations

DNA double helix, A-T and C-G pairing, nuclear vs mitochondrial inheritance, ~6.6 pg per diploid cell, and tetranucleotide STR repeat structure.

Workflow

Extraction, Quantitation, Amplification

Chelex 100, organic phenol-chloroform, magnetic-bead (DNA IQ, PrepFiler) extraction; Quantifiler Trio degradation index and IPC; PCR thermocycling, ~28-29 cycles for routine STR, stutter (<15% for tetra), +A/-A, and PCR inhibitors.

Detection

Capillary Electrophoresis and STR Typing

ABI 3500xL/3130xl, 6-dye kits (GlobalFiler, Fusion 6C), POP-4 polymer, GS500/600 LIZ size standard, the 20 CODIS core loci as of January 2017, amelogenin, Y-indel, and miniSTRs.

Interpretation

Profile and Mixture Interpretation

Analytical threshold (often ~50 RFU after validation), stochastic threshold (often ~150-200 RFU), PHR, drop-out, drop-in, SWGDAM NoC logic, and probabilistic genotyping with STRmix, TrueAllele, and EuroForMix.

Statistics

Population Genetics and Statistics

Hardy-Weinberg 2pq heterozygote frequencies, NRC II theta corrections, RMP across loci, LR and Hp/Hd framing, CPI/CPE limitations, and prosecutor's-fallacy avoidance.

Specialized

Lineage Markers and Emerging Methods

Y-STR (Yfiler Plus 27 loci, PowerPlex Y23), mtDNA HV1/HV2 vs rCRS, heteroplasmy, identity/ancestry/phenotype SNPs, MPS/NGS, and Investigative Genetic Genealogy (GEDmatch, FamilyTreeDNA, DOJ Interim Policy).

Quality Assurance, CODIS, Ethics

FBI QAS casework and databasing standards, ISO/IEC 17025, OSAC Biology Subcommittee, NIST SRM 2391d, CODIS LDIS/SDIS/NDIS architecture, technical and administrative review, semi-annual external proficiency testing, and ABC Rules of Professional Conduct.

How to Pass the ABC Forensic DNA Exam

What You Need to Know

Passing score: Cut score set by ABC during exam development; numeric value not disclosed to candidates
Exam length: 90 questions
Time limit: 2 hours 15 minutes
Exam fee: $75 application + $250 examination sitting + $100 annual recertification maintenance

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ABC Forensic DNA Study Tips from Top Performers

1Anchor study to the ABC Forensic DNA Examination Blueprint and DACUM chart from criminalistics.com before grinding practice questions.

2Memorize the 20 CODIS core loci as of January 2017 (D8S1179, D21S11, D7S820, CSF1PO, D3S1358, TH01, D13S317, D16S539, D2S1338, D19S433, vWA, TPOX, D18S51, D5S818, FGA, D1S1656, D2S441, D10S1248, D12S391, D22S1045) plus amelogenin, Y-indel, and SE33.

3Drill Hardy-Weinberg formulas (2pq, p^2 + p(1-p)*theta), NRC II theta values, and the difference between CPI/CPE and LR for mixtures.

4Practice translating Quantifiler Trio results (small target, large target, Y-target, IPC) into casework decisions about template dilution, degradation index, mixture composition, and inhibition.

5Re-read SWGDAM interpretation guidelines, ISFG LR position papers, and current OSAC Biology standards; questions test their wording, not just concepts.

6Run probabilistic genotyping case studies in STRmix, TrueAllele, or EuroForMix (or worked examples) so Hp/Hd, NoC, and continuous models are intuitive.

7Review the FBI Quality Assurance Standards section by section (validation, controls, audit, proficiency testing, technical review) and tie each section to a real-lab artifact you can describe in court.

Frequently Asked Questions

Who is eligible to sit for the ABC Forensic DNA specialty exam?

Candidates must be actively employed in a forensic DNA laboratory and meet the FBI Quality Assurance Standards (QAS) education, training, and experience requirements for casework or databasing DNA analysts. ABC also requires the application packet, references, and Rules of Professional Conduct attestation.

How many questions are on the ABC Forensic DNA exam and how long is it?

The Forensic DNA specialty exam (ABC-DNA) contains 75 scored questions plus 15 pilot (unscored) items for a total of 90 items, with a maximum testing time of 2 hours 15 minutes.

How much does the ABC Forensic DNA certification cost?

ABC charges a $75 application fee and a $250 examination sitting fee. After certification, an annual recertification maintenance fee of $100 is due by March 1 each year (escalating to $150 and $275 with late penalties).

Is the ABC Forensic DNA exam the same as the older ABC Molecular Biology (ABC-MB) certification?

ABC's currently offered DNA-related specialty exam is the Forensic DNA (ABC-DNA) examination, which is the current pathway. Legacy Molecular Biology (ABC-MB) certificants who remain in good standing retain their certified status.

How is the ABC Forensic DNA exam scored?

Each exam has a cut score determined during development and pilot testing; ABC does not publicly disclose the numeric passing percentage. Only the 75 scored questions count toward the result; the 15 pilot questions are not graded.

What topics are tested on the ABC Forensic DNA specialty exam?

The exam covers DNA structure and inheritance, sample workflow (extraction, quantitation, PCR), CE-based STR typing using the 20 CODIS core loci, mixture interpretation with probabilistic genotyping, Y-STR and mtDNA lineage markers, population genetics and statistics, FBI QAS quality assurance, CODIS rules, and emerging technologies such as MPS and Investigative Genetic Genealogy.

Is the ABC Forensic DNA exam available via remote proctoring?

No. ABC examinations, including the Forensic DNA specialty exam, are administered in person at approved testing locations only. ABC does not offer remote proctoring.

How often must I recertify the ABC Forensic DNA credential?

ABC certificates expire on the fifth anniversary of certification. Certificants pay the annual maintenance fee, accumulate documented continuing-education and professional-development points across the 5-year window, and submit the Rules of Professional Conduct attestation before the cycle ends.

Does ABC publish the pass rate for the Forensic DNA exam?

No, ABC does not publish first-time pass-rate percentages for the Forensic DNA specialty exam. Candidates receive a pass/fail result with category-level feedback.