Forensic Genetics Quiz

What is a typical limitation of Y-STR profiles?. They do not distinguish males belonging to the same paternal line. They are biallelic and therefore less informative than SNPs.

Distinguish between polymorphism and mutation in a population and forensic context, providing practical examples. Polymorphism is a variation within a population, while mutation is a change in DNA sequence. Mutation is a change in DNA sequence that leads to polymorphism within a population.

Define mitochondrial heteroplasmy and discuss its implications in forensic settings. Heteroplasmy refers to the presence of multiple variants of mtDNA within the same cell, which can complicate analysis. Heteroplasmy means that all mitochondria in a cell are identical.

Describe the utility of Y-STRs in mixtures with a female prevalence and their interpretative limitations. Y-STRs are useful for identifying the male contributor in samples with a high proportion of female DNA, but limitations include the potential for allele dropout and difficulty in interpreting complex mixtures. Y-STRs are not useful in mixtures with female prevalence.

Explain why SNPs are particularly suitable for analyzing highly degraded DNA and what statistical considerations are needed for comparable discriminating power to STRs. SNPs, due to their small amplicon size, are more resilient to degradation. To achieve comparable discrimination to STRs, a large number of SNPs need to be analyzed. SNPs are not suitable for degraded DNA.

Assortment + crossing-over produce: More heterozygosity. Rarer profiles.

Why don't we analyze 'all the DNA'?. It's too identical, we aim for polymorphisms. Primers do not exist.

Locus means... Position on the chromosome. Expressed gene.

What is the Allelic ladder used for?. To translate lengths into alleles. To reduce stutter.

LR compares: H1 vs H2 on data. CE vs PCR.

The flanking regions of STRs are used to: Anchor PCR to the locus. Color the peaks.

RMP measures: The random coincidence of a profile. The rarity of the fluorophore.

A genotype of 10/10 is: Homozygous. Heterozygous.

Explain what Random Match Probability (RMP) and Likelihood Ratio (LR) represent. RMP is the probability of a random match, while LR compares the likelihood of evidence under different hypotheses. RMP and LR are the same statistical measure.

Illustrate the meaning of 'locus independence' and how independent assortment and recombination during meiosis ensure high discriminatory power of multi-locus profiles. Locus independence means alleles at different loci are inherited independently, leading to a high combined probability of identification. Locus independence means all loci are on the same chromosome.

Explain the difference between homozygosity and heterozygosity at an STR locus. Homozygosity means having two identical alleles, while heterozygosity means having two different alleles at a locus. Homozygosity means having different alleles, and heterozygosity means having identical alleles.

In ISFG allelic nomenclature, the notation '14.2' indicates: 14 complete repeat units and one partial repeat of two bases. 14 alleles in the panel.

Genetic independence between STR loci allows us to: Apply the product rule for calculating the overall profile probability. Reduce the number of loci analyzed.

Which parameter indicates the probability that two individuals share the same STR profile by chance?. Random Match Probability (RMP). Likelihood Ratio (LR).

In STR analysis of highly degraded DNA, which strategy is most effective?. Use miniSTR kits with primers closer to the repeat region. Increase the concentration of MgCl2 in the PCR.

Y-chromosome STRs are primarily used for: Identifying the male contribution in mixed traces. Studying mitochondrial mutations.

Which of the following statements correctly describes a microvariant?. An allele with an incomplete or partial repeat unit. A repetition inserted in a gene intron.

What molecular mechanism generates variability in the number of STR repeats?. Slippage of DNA polymerase during replication. Homologous recombination between chromosomes.

The presence of multiple individuals in a biological sample entails: The formation of mixed profiles with multiple peaks for each locus. The appearance of a single average peak per locus.

Explain why STRs are preferred markers over minisatellites in forensic analysis. STRs have shorter amplicon sizes leading to better separation and are more suitable for degraded DNA. Minisatellites are not polymorphic.

Describe the structure of an STR locus and how allelic nomenclature is assigned, including the concept of microvariant. An STR locus consists of a core repeat unit and flanking regions. Nomenclature assigns numbers based on repeat units, with microvariants indicating partial repeats. STR loci have a fixed number of repeats.

Illustrate what stutter are in STR analysis and why tetranucleotides are preferred in forensic kits. Stutter are artifact peaks caused by polymerase slippage during PCR. Tetranucleotides are preferred because they produce less stutter and have more distinct alleles. Stutter are the main STR alleles.

Explain the principle of multiplex-PCR for STRs and the role of the allelic ladder in interpreting the electropherogram. Multiplex-PCR amplifies multiple STR loci simultaneously. The allelic ladder is a size standard to identify alleles based on fragment length. Multiplex-PCR amplifies only one STR locus at a time.

Which of the following statements about satellite DNA is correct?. It consists of non-coding repetitive sequences with structural functions in chromosomes. It is exclusively a mitochondrial DNA region.

What was the main limitation of RFLP analysis on VNTRs?. It required large amounts of intact DNA and long analytical times. It was based on multiple PCR amplification.

Which of the following characteristics most distinguishes SNPs from STRs?. SNPs are point variations, not length differences. SNPs change more rapidly over time.

What is the main statistical advantage of multiple SNP panels?. Increase the combinatorial probability of identification. Require only one allele per genotype.

In forensic analysis, mitochondrial SNPs are used to: Trace the maternal lineage in the absence of usable nuclear DNA. Analyze the paternal line in male genealogies.

Forensic phenotyping based on SNPs allows: Prediction of traits like eye color, skin, and hair color. Certain identification of a subject.

Y-specific SNPs primarily have applications in: Studies of paternal line and male genealogical analyses. Determination of visual phenotypes.

Alpha-satellite DNA is located: In the centromeres, where it contributes to kinetochore formation. In telomeres, where it regulates gene transcription.

Describe what is meant by satellite DNA and its structural functions in centromeres and telomeres. Satellite DNA consists of highly repetitive, non-coding sequences that provide structural integrity and facilitate chromosome segregation at centromeres and telomeres. Satellite DNA encodes proteins essential for cell function.

Define SNPs and compare them with STRs in terms of polymorphism nature and informativeness per locus. SNPs are single nucleotide changes (point mutations), while STRs involve variations in repeat number. STRs are generally more informative per locus than SNPs. SNPs are more informative per locus than STRs.

Explain why SNPs, due to the reduced amplicon size, are indicated for highly degraded DNA. Smaller DNA fragments are more likely to survive degradation. SNPs are less susceptible to PCR inhibition.

Reconstruct the historical progression from VNTR/RFLP (satellite DNA) to STR and the current integrative role of SNPs. VNTR/RFLP was an early method using satellite DNA; STRs improved efficiency and sensitivity; SNPs offer high throughput and utility in degraded DNA. STRs replaced VNTRs entirely and SNPs are not used in forensics.

What is the primary reason why mitochondrial DNA is inherited solely from the mother?. Maternal mitochondria fuse with paternal mitochondria. Paternal mitochondria are located in the sperm tail, which does not enter the ovum.

In comparing an unknown and a reference mtDNA, the presence of a single difference implies: Exclusion. Inconclusive result.

What is the primary function of the mitochondrion in a eukaryotic cell?. Energy production in the form of ATP. Synthesis of essential amino acids.

What is meant by mitochondrial bottleneck?. The temporary reduction in the number of mitochondria during germ cell formation. The fusion of maternal and paternal mitochondria.

How many base pairs make up human mitochondrial DNA?. Approximately 16,569. Approximately 1,569.

Why is mitochondrial DNA useful in forensic analysis?. It is present in multiple copies per cell. It is highly degradable.

Where are the hypervariable regions HV1 and HV2 of mtDNA located?. In the D-loop, the non-coding control region. In protein-coding regions.

What does the term heteroplasmy indicate?. The coexistence of multiple mtDNA variants within the same cell. The complete absence of genetic variability in mtDNA.

Describe the characteristics and role of the hypervariable regions HV1 and HV2 in a forensic context. HV1 and HV2 are highly variable regions within the mtDNA control region, useful for distinguishing individuals due to their high mutation rate. HV1 and HV2 are highly conserved regions.

Summarize the advantages and limitations of using mitochondrial DNA in forensic investigations. Advantages: high copy number, maternal inheritance useful for lineage tracing. Limitations: lower discrimination power than nuclear DNA, potential for heteroplasmy. Advantages: high discriminatory power. Limitations: only inherited paternally.

Why is mitochondrial DNA inherited exclusively maternally?. The sperm's mitochondria are typically degraded or excluded after fertilization. Maternal mtDNA recombines with paternal mtDNA.