MLT GlobeForensic Science: Forensic DNA & identification – page 2
40 Forensic Science MCQs on Forensic DNA & identification with answers and explanations.
What is the main advantage of mini-STRs?
Primers placed close to the repeat region reduce amplicon size, so more templates remain intact in degraded samples, such as old bones.
Why is DNA quantified by real-time PCR before STR amplification?
qPCR estimates amplifiable human (and male) DNA so the optimal input is used. Internal controls and degradation indices guide further testing.
What is the purpose of differential extraction on a vaginal swab?
Epithelial cells lyse first with detergent and proteinase K. Sperm heads, stabilised by disulphide bonds, then lyse with DTT, giving male-enriched fractions.
What is a characteristic of DNA extracted by the Chelex-100 method?
Boiling with Chelex chelates metal ions and denatures DNA. The single-stranded product is fine for PCR but unsuitable for RFLP.
What does the random match probability of a single-source DNA profile express?
RMP is estimated with population allele frequencies and the product rule. It is not the probability of guilt, a common misinterpretation (prosecutor's fallacy).
In paternity testing, why is an exclusion usually reported only when inconsistencies occur at several loci?
STR mutation rates are around 0.1–0.3% per locus per generation. A single mismatch is evaluated with mutation-adjusted indices; multiple inconsistencies support exclusion.
Which hair provides the best chance of a nuclear DNA STR profile?
Actively growing anagen roots carry nucleated follicular tissue. Shed telogen hairs and shafts usually yield only mtDNA.
Ninhydrin develops latent fingerprints on porous surfaces such as paper by reacting with what?
Amino acids from sweat absorb into paper and react with ninhydrin to form a purple product, which can be enhanced further.
Which technique is commonly used to develop latent prints on non-porous surfaces like glass or plastic?
Cyanoacrylate vapour polymerises on print residues, forming a white deposit that can be dyed and viewed under alternate light.
What is the standard methodology for friction ridge comparison?
Examiners analyse the latent, compare it with an exemplar, evaluate for a conclusion, and have a second examiner verify.
Which skeletal element is most reliable for estimating the sex of adult remains?
The pelvis reflects adaptations for childbirth, such as a wider sub-pubic angle and greater sciatic notch, and gives the highest accuracy.
Stature is estimated from skeletal remains mainly using regression equations applied to which bone?
Long bones of the leg correlate strongly with height. The femur is widely used, with population-specific regression formulae.
A known male shows only the X peak at amelogenin in an STR profile. What is the best explanation and follow-up?
Rare males carry deletions removing AMELY. Additional Y markers, such as Y-STRs or kit loci like DYS391, confirm male DNA.
A very low-template sample shows a heterozygote with one allele missing at some loci. Which phenomenon explains this?
With few template copies, random sampling during early PCR cycles can amplify one allele preferentially, causing peak imbalance or complete drop-out.
In a qPCR quantification, the internal PCR control is delayed while human DNA is detected. What does this indicate?
The internal control amplifies a synthetic target added to every reaction. Delayed or failed control amplification signals inhibition, prompting cleanup or dilution.
What is the main feature of fully continuous probabilistic genotyping software used for complex mixtures?
Continuous models (e.g., STRmix, TrueAllele) incorporate peak heights, stutter, drop-out and drop-in to calculate a likelihood ratio comparing prosecution and defence propositions.
How is the combined paternity index (CPI) obtained from individual locus paternity indices?
Loci are inherited independently, so their likelihood ratios are multiplied to give the combined index.
With a neutral prior probability of 0.5, how is the probability of paternity (W) calculated from the CPI?
Using Bayes' theorem with prior odds of 1, posterior odds equal CPI, and probability = CPI/(CPI+1). For CPI 1000, W ≈ 99.9%.
A missing person has no direct antemortem DNA sample. Which reference is most informative for kinship identification?
Both parents together define the possible alleles at every locus, giving strong likelihood ratios. Spouses and adopted children share no inherited DNA.
Which skeletal sample generally gives the highest DNA yield from old or degraded remains?
The dense petrous bone protects DNA well and consistently outperforms other elements; dense femoral cortex and teeth are also good choices.