HSC Exam Practice

Sample response. DNA sequencing is the determination of the exact order of nucleotide bases (A, T, C and G) in a DNA region or whole genome.

Marking notes. 1 mark for identifying that sequencing determines base order; 1 mark for naming nucleotide bases / referring to DNA region or genome.

Sample response. DNA profiling is the comparison of patterns at selected DNA marker regions between samples, used to distinguish or relate them.

Marking notes. 1 mark for comparison at selected marker regions; 1 mark for identifying its purpose (distinguish / relate / match samples).

Sample response. DNA sequencing produces an ordered string of nucleotide bases — the actual sequence of the region. DNA profiling produces a pattern of bands or peaks at selected marker regions, not the underlying base order. As a result, sequencing can identify a specific inherited variant directly, while profiling indicates similarity or difference at chosen markers.

Marking notes. 1 mark for output of sequencing (base order / ordered string); 1 mark for output of profiling (marker pattern); 1 mark for naming a consequence of the difference (e.g. only sequencing identifies the specific base change).

Sample response. Identifying the specific inherited base change responsible for a disease (for example, a known disease-linked SNP) requires sequencing, because only sequencing reads the actual nucleotide at that position. Profiling shows fragment-size pattern similarity, not the base itself.

Marking notes. 1 mark for naming a sequencing-appropriate question (variant identification / SNP detection / mutation characterisation); 1 mark for justification linking to base-order output.

Sample response. A DNA profile compares patterns at a small set of selected marker regions and does not read the base order at the rest of the genome. Equating a profile with a full genome sequence overstates what profiling produces — it conflates pattern matching at selected loci with whole-genome base-order determination.

Marking notes. 1 mark for identifying that profiling examines only selected markers; 1 mark for stating that base order at the rest of the genome is not read.

Sample response. DNA sequencing reads base order, so it can identify specific inherited variants (such as disease-linked SNPs) and measure how their frequencies vary across populations. DNA profiling compares patterns at selected DNA markers, so it can support inferences about relatedness, lineage and shared inheritance between samples. Together, the two technologies build a picture of inheritance patterns within and between populations.

Marking notes. 1 mark for sequencing's contribution (variant / allele-frequency identification); 1 mark for profiling's contribution (relatedness / sample comparison); 1 mark for linking both to inheritance-pattern inference in populations.

Sample response (a). Sample X carries the disease-linked variant — at position 11 it reads G where the reference reads A, matching the A→G disease-linked change. Sample Y carries only the neutral polymorphism — at position 11 it reads A (matching reference) and at position 17 it reads T where the reference reads C, matching the C→T neutral polymorphism.

Sample response (b). Drawing this conclusion requires reading the actual nucleotide at positions 11 and 17. Sequencing produces the base order directly, so each position can be inspected. DNA profiling would only compare patterns at selected marker regions and would not reveal the actual base present at any given position, so neither the disease variant nor the neutral polymorphism could be distinguished from profiling output alone.

Sample response (c). 500 individuals contribute 2 × 500 = 1,000 alleles. 12 individuals each carry one copy of the variant, contributing 12 variant alleles in total. Allele frequency = 12 / 1,000 = 0.012 (or 1.2%).

Marking notes. Part (a) — 1 mark for correctly identifying X as the disease-variant carrier with position-11 reference to G; 1 mark for correctly identifying Y as the neutral-polymorphism carrier with position-17 reference to T. Part (b) — 1 mark for stating sequencing reads actual base at each position; 1 mark for noting profiling does not show base order. Part (c) — 1 mark for correct total allele count (1,000); 1 mark for correct frequency (0.012 / 1.2%). Award full marks for equivalent calculations with stated assumptions.

Sample response. DNA sequencing and DNA profiling are related but distinct technologies that both contribute to investigating inheritance patterns in populations. Sequencing determines the exact order of nucleotide bases in a DNA region, producing an ordered string of As, Ts, Cs and Gs. Profiling, by contrast, compares patterns at selected DNA marker regions between samples, producing a band or peak pattern rather than the underlying base order. The two outputs answer different kinds of question. Because sequencing reads the actual base at each position, it can identify a specific inherited variant directly — for example, screening members of a population for a known disease-linked SNP such as the cystic-fibrosis ΔF508 variant in the CFTR gene, or characterising novel mutations in inherited disorders. This makes sequencing the appropriate technology for variant discovery and for estimating how often a specific allele appears in a population. Profiling, by contrast, is the appropriate technology for sample comparison: STR profiling at multiple marker loci can support inferences about relatedness between individuals or families — including paternity testing, lineage tracking, and forensic identity comparison such as the use of profile matching during the 2005 Northern Territory prosecution of Bradley John Murdoch. Each technology has limits. Sequencing is more expensive and more data-intensive per individual; profiling cannot, on its own, identify the actual base change responsible for an inherited trait. The most powerful population-inheritance studies use both technologies in combination: profiling to compare and group samples, then sequencing to characterise the variants behind any pattern of interest. Therefore, neither technology is universally superior — the choice depends on the inheritance-pattern question being asked, and both contribute complementary evidence to our understanding of inheritance in populations.

Marking notes. 1 mark — defines DNA sequencing as determination of base order. 1 mark — defines DNA profiling as comparison of patterns at selected marker regions. 1 mark — contrasts the two outputs with one consequence (e.g. only sequencing reads actual base). 1 mark — identifies the kind of inference sequencing supports (variant identification, allele-frequency estimation). 1 mark — identifies the kind of inference profiling supports (relatedness, sample comparison). 1 mark — uses a named application of sequencing (e.g. CFTR disease-variant screening / SNP frequency study). 1 mark — uses a named application of profiling (e.g. forensic identity comparison or paternity testing). 1 mark — reaches an explicit evaluative judgement linking the choice of technology to the inheritance-pattern question being investigated (purpose-dependent, complementary technologies). Award full marks for equivalent responses with appropriate examples.