D1.1.5—Applications
Applications of DNA replication techniques use PCR, gel electrophoresis and DNA profiles to identify individuals, test paternity and support forensic or medical decisions.
- Syllabus
- First assessment 2025
- Objective
- D1.1.5
- Level
- SL
Exam analysis
Chance of appearing4%of analysed past papers
Latest appearanceNovember 2023
Most common paperPaper1
Typical marks1–4
Common command terms
- Identify
- Determine
- Explain
- Describe
- Outline
Scoring notes
- Common mistake
- Confusing DNA polymerase I primer replacement with DNA polymerase III strand elongation.
Recent exam appearances
November 2023Paper1 ["SL"] · TZ117[ 1 ]D1.1.5—Applications
May 2015Paper2 ["SL"] · TZ16(b)[ 5 ]D1.1.5—Applications
May 2014Paper2 ["SL"] · TZ16(c)[ 4 ]D1.1.5—Applications
May 2013Paper1 ["SL"] · TZ217[ 1 ]D1.1.5—Applications
November 2010Paper1 ["SL"] · TZ018[ 1 ]D1.1.5—Applications
Practice this objective
Coverage 2010–2023 · Updated 16 Jul 2026
DNA Profiles Compare Variable Fragment Patterns
PCR and gel electrophoresis support DNA profiling by amplifying and comparing variable DNA markers.
In a paternity investigation, a child's marker alleles must be explainable by the biological parents. In a forensic investigation, a crime-scene DNA pattern can be compared with reference samples.
Use several independent markers: each additional matching marker reduces the probability that an unrelated person shares the full pattern by chance. Include positive/negative controls and guard against contamination.
A child's allele not supplied by the known parent must match the candidate parent's allele at each tested marker; one matching marker is weak, whereas a consistent multi-marker pattern is stronger evidence.
A profile supports or excludes a biological relationship/source; it does not alone prove when or how DNA reached a location. More markers reduce false-match probability but do not make laboratory error impossible.
Applications exam focus
Assessment in practice
1–4 marksHow it is assessed
This objective is assessed through structured response, commonly using Identify / Determine / Explain.
Command terms
Identify / Determine / Explain / Describe / Outline
What earns marks
Build the answer around this relationship: Applications depends on matching each strand, enzyme or laboratory step to its exact function.
Watch for
Confusing DNA polymerase I primer replacement with DNA polymerase III strand elongation.
Representative question
Question 1
Outline the process of DNA profiling.
Core DNA Replication
DNA replication produces exact DNA copies before cell division and maintains genetic continuity for reproduction, growth, and tissue replacement. Semi-conservative replication gives each new DNA molecule one original strand and one new strand; complementary base pairing and Meselson-Stahl isotope evidence support the model. Helicase unwinds DNA and breaks hydrogen bonds; DNA polymerase joins complementary nucleotides to build new strands. PCR amplifies selected DNA using primers, temperature cycles, and Taq polymerase; gel electrophoresis separates DNA fragments by size and charge. PCR and gel electrophoresis support DNA profiling for forensic identification and paternity testing.
Concept essentials
- Applications depends on matching each strand, enzyme or laboratory step to its exact function.
- Template strands and complementary base pairing give applications its copying accuracy.
- Applications is clearer when amplification, separation and profiling are not confused.
- Molecular evidence for applications must be interpreted from bands, isotopes, primers or enzyme roles.