Forensic Genetics Quiz: DNA and Chromosomes

What is the function of telomeres?. Protect chromosome ends from fusion and inappropriate repair. Facilitate centromere pairing.

What is satellite DNA?. A centromeric LINE. A pericentromeric SINE. A centromeric tandem repeat.

Which group does interspersed repetitive DNA belong to?. Microsatellites (STR). LINE-1, SINE/Alu, LTR/ERV. Alpha-satellite. Minisatellites (VNTR).

Where is alpha-satellite DNA mainly located and what is its key role?. Subtelomeres; caps against fusion. Promoters; direct transcriptional control. Centromeres; scaffold for kinetochore and microtubule attachment. Pericentromeres; meiotic recombination.

What advancement did the T2T consortium achieve in 2022 compared to the 2003 reference?. Complete gapless sequence (including centromeres) with error correction. First draft of the human genome. Closure of the mtDNA. Reduction of gene number to <10,000.

What practical benefits arise from knowledge of genomic architecture in various fields?. All other answers are correct. Targeted therapies in oncology. Diagnosis/pharmacogenomics in clinics. Choice of STR/SNP panels in forensics.

Which statement about STRs is correct?. They are located exclusively in genes. No correct answer. They are repeats of 2-6 bp, highly polymorphic, with tetranucleotides preferred. They are repeats of 10-20 bp, highly polymorphic, with trinucleotides preferred.

What are the two main ways pseudogenes are formed?. Deamination and transversions. Replicative slippage and homologous recombination. Duplication followed by inactivation; retrotransposition (exonless copy). Crossing-over and non-disjunction.

Which elements are among the main interspersed repetitive sequences?. Microsatellites, minisatellites, telomeres. Telomeres, centromeres, HOR. LINE-1, SINE/Alu, LTR/ERV. Autosomal STRs.

What percentage of the human genome is directly protein-coding?. 10%. None of the other answers. 50%. 25%.

What is the approximate size of the diploid human genome?. ~3.2 billion bp. ~1.2 Gbp. ~6.4 billion bp. ~320 million bp.

What is the approximate size of the haploid human genome?. ~320 million bp. ~6.4 billion bp. ~1.2 Gbp. ~3.2 billion bp.

What does the human genome in somatic cells comprise?. Nuclear DNA (46 chromosomes) and mitochondrial DNA. Only linear nuclear DNA. Nuclear DNA with 23 chromosomes. Only circular mitochondrial DNA.

What is a practical limitation of VNTR typing using RFLP/Southern that favored the shift to STR-PCR?. VNTRs are too short for reliable PCR amplification. RFLP requires large amounts of DNA, which is often degraded. The longer repeat units of VNTRs lead to complex banding patterns. VNTRs are not polymorphic enough for forensic identification.

Where is alpha-satellite DNA mainly located and what is its key function at the chromosomal level?. Telomeres; protecting chromosome ends. Centromeres; providing a scaffold for kinetochore assembly. Pericentromeres; facilitating meiotic recombination. Genes; regulating gene expression.

Define a VNTR (minisatellite), indicating the approximate size of the repeat unit and what varies between alleles. Repeat unit of 2-6 bp; variation in the number of repeats. Repeat unit of 10-20 bp; variation in the DNA sequence of the repeat. Repeat unit of tens to hundreds of bp; variation in the number of repeats. Repeat unit of <10 bp; variation in the number of repeats.

What distinguishes Anaphase II from Mitotic Anaphase?. Separation of chromatids in a haploid set. Separation of homologs. Duplication of chromatids. Chromatin condensation.

What is the effect of crossing-over in Prophase I?. Allelic recombination between sister chromatids. Duplication of centromeres. Reduction of genetic variability. Allelic recombination between homologous chromosomes.

In which phase of the cell cycle does DNA duplication occur?. S phase. G1 phase. G2 phase. M phase.

What characterizes the G2 phase before entering mitosis?. Separation of chromatids. G1/S checkpoint. Control of duplicated DNA in G2/M. Crossing-over.

What is the correct distinction between Meiosis I and Meiosis II?. Both separate homologs. None of the other answers. Meiosis I: chromatids; Meiosis II: homologs. Meiosis I: homologs; Meiosis II: sister chromatids.

Why are autosomal STR loci selected on different or distant chromosomes?. To approximate locus independence and combine probabilities. To avoid the use of PCR. To increase linkage between markers. None of the other answers.

What is the main function of cohesins?. To compact chromosomes in prophase. To form the kinetochore. To lengthen telomeres. To hold sister chromatids together.

What event marks the anaphase of mitosis?. Formation of chiasmata. Double DNA breakage. Separation of sister chromatids. Alignment at the metaphase plate.

In which phase is independent assortment operationally realized?. Metaphase I. Telophase I. Prophase I. Anaphase II.

Which process, along with assortment, increases gamete variability?. Crossing-over. Repair. None of the other answers. Telomere shortening.

What is meant by genetic variability in the context of forensic genetics?. Only phenotypic differences observable between individuals, independent of DNA. Only numerical chromosomal variations (aneuploidies) found in a population. None of the other answers. The set of heritable differences in DNA between individuals, originating from mutations and reshuffled by recombination, and modulated by migration, drift, and selection.

Regarding STRs used in forensics, what differs between individuals at the same locus?. The nature of the chromosome. The chromosomal coordinates of the locus. All other answers are correct. The number of repeat units of the tandem motif.

In population genetics, when is a variant defined as a polymorphism?. When its frequency is at least 1% in the reference population. When it causes a measurable pathological effect. When it has been observed at least once as a de novo event. When it appears in at least 10% of individuals in any population.

In the human genome, where does the majority of polymorphisms occur relative to functional regions?. In non-coding regions (intergenic and introns). Predominantly in exons that code for proteins. Almost exclusively in promoters and enhancers. In mitochondrial DNA.

What is a key technical advantage of SNPs over STRs in degraded samples?. They always allow individual identification without statistical models. They are multi-allelic markers with higher discriminating power per single locus. They require very short amplicons (often <100 bp), making them more robust in fragmented DNA. 10 markers are sufficient for identification.

To achieve a power of identification comparable to modern STR profiles, how many informative and independent SNPs are typically needed?. Not less than 1000 SNPs, otherwise the RMP is always > 10^-2. Over 50 SNPs selected for high heterozygosity and low correlation. About 5-10 SNPs, because each is highly multi-allelic. A single SNP with an amplicon <60 bp is sufficient in degraded samples.

Which statement correctly summarizes the forensic use of mtDNA?. It is inherited only maternally, has many copies per cell, and is useful on degraded samples; it does not individualize among close maternal relatives. It is inherited equally from mother and father and recombines each generation. It always has greater discriminating power than autosomal STRs. All other answers are correct.

What is a typical probative limitation of Y-STR profiles?. None of the other answers. They do not distinguish males belonging to the same paternal line. They are sensitive to the female component and tend to lose alleles in mixtures with female prevalence. They are biallelic and therefore less informative than SNPs.

Distinguish between polymorphism and mutation in population and forensic contexts, providing practical examples. A mutation is a new change, while a polymorphism is an established, common variant. A mutation is always harmful, while a polymorphism is neutral. Polymorphisms are only found in coding regions, while mutations can be in non-coding regions. Mutations are only observed in rare diseases, while polymorphisms are common in all populations.

Define mitochondrial heteroplasmy and discuss its implications in forensic contexts (HV regions, length heteroplasmy, advantages and limitations of mtDNA evidence). Heteroplasmy is the presence of multiple mtDNA types within a single cell or individual, which can complicate interpretation but is useful for tracing maternal lineages. Heteroplasmy refers to mutations in the mitochondrial DNA that are always passed to offspring. Heteroplasmy in HV regions indicates the presence of nuclear DNA contamination. Length heteroplasmy is primarily caused by nuclear DNA recombination.

Describe the utility of Y-STRs in mixtures with a female prevalence and the main interpretative limits, including the role of 'fast' loci and the inclusion of mutation rates in calculations (LR). Y-STRs can help identify the male contributor in mixtures where females are present, but they cannot differentiate between males in the same paternal lineage and require careful consideration of mutation rates for accurate likelihood ratio calculations. Y-STRs are not useful in female-prevalent mixtures because they only amplify male DNA. Fast loci in Y-STRs significantly increase discrimination power between closely related males. Mutation rates are generally ignored in Y-STR analysis due to their low variability.

Explain why SNPs are particularly suitable for the analysis of highly degraded DNA and what statistical considerations are necessary to achieve a discriminating power comparable to STRs. SNPs require short amplicons, making them robust in degraded DNA. To match STR power, a large number of independent SNPs are needed, with calculations often using algorithms that account for linkage disequilibrium. SNPs are only useful for degraded DNA because they are less polymorphic than STRs. Degraded DNA analysis with SNPs does not require any special statistical considerations. The short length of SNP amplicons makes them less informative, so statistical power cannot be matched to STRs.