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Q: What does H2 Biology Notes (9477, 2026): Core Idea 2 - Genetics & Inheritance cover? A: Master DNA architecture, chromatin control, genetic exchange in microbes, meiotic variation, and multi-gene inheritance so you can tackle 2026 H2 Biology genetics essays and data tasks with confidence.
TL;DR Use this Core Idea 2 guide to lock in DNA structure + gene regulation, microbial genetics, meiosis, inheritance
patterns, and chi-squared/data skills that show up across Papers 2–4.
Status: Updated for SEAB H2 Biology (9477, first exam 2026); syllabus last checked 2026-01-12. [1]
Why genetics drives Paper 2, Paper 3, and Paper 4
Breadth of questioning: Paper 2 (2 h, 30%) and Paper 3 (2 h, 35%) pull Core Idea 2 content-from DNA replication and gene regulation to mutation and cancer essays-into structured and long-response prompts.
Data handling: Paper 4 (2 h 30 min, 20%) assesses planning plus MMO/PDO/ACE; chi-squared checking of observed vs expected ratios sits in Core Idea 2 learning outcomes.
Links across syllabus: Viral and bacterial genetics, regulation from chromatin to operons, and inheritance patterns sit in Core Idea 2 of the SEAB 9477 (first exam 2026) syllabus, feeding directly into evolution and biotechnology questions. [1]
Syllabus snapshot
DNA structure, chromatin levels (nucleosome to metaphase chromosome)
Central dogma: replication, transcription, translation, and regulation
Viral and bacterial genetics: lytic/lysogenic cycles, horizontal gene transfer
Genome organisation, mutations, and cancer genomics
Cell cycle control, mitosis, and meiosis
Mendelian, non-Mendelian, and multi-factorial inheritance
Quantitative skills: chi-squared tests for segregation ratios
), complementary base pairing (A–T via two hydrogen bonds, G–C via three). Emphasise phosphodiester backbone directionality for referencing replication enzymes. [2]
Chromatin packaging: Progress from nucleosome (“beads on a string”) to higher-order packing such as a 30 nm chromatin fibre, loops, and metaphase chromosome. [2] Discuss histone tail acetylation (often relaxes chromatin and promotes transcription) and methylation (context-dependent) as part of chromatin-level regulation. [2]
Genome organisation: Contrast exons, introns, centromeres, telomeres, and regulatory sequences (promoters, enhancers, silencers). Note that prokaryotic genes typically lack introns and are often arranged in operons. [2]
Practice sketch
Draw and annotate a nucleosome, labelling DNA directionality and indicating how histone acetylation alters transcriptional accessibility.
Concept 2: Flow of genetic information
Replication: Semi-conservative replication with origins, replication forks, leading and lagging strands. Highlight enzymes such as helicase, primase, DNA polymerase, ligase, and topoisomerase. [2] (In bacteria, DNA polymerase III synthesises most of the new DNA and DNA polymerase I helps replace primers-details not required unless a question specifies prokaryotic replication.) [2] Stress proofreading and mismatch repair, and flag the end-replication problem on lagging strands and the telomerase solution. [2]
Transcription and RNA processing: RNA polymerase binding to promoter (often involving a TATA box in eukaryotes), formation of pre-mRNA, 5’ capping, polyadenylation, and splicing (spliceosome). [2] Introduce alternative splicing for proteome diversity. [2]
Translation: Initiation (small ribosomal subunit binds mRNA; initiator tRNA enters the P site), elongation (codon–anticodon pairing, peptidyl transferase), termination (release factors). [2] Distinguish 80S eukaryotic vs 70S prokaryotic ribosomes. [2]
Gene regulation: Describe transcription factors, enhancers, silencers, and DNA methylation. [2] Compare prokaryotic operon control-lac operon (inducible) vs trp operon (repressible). [2]
DNA analysis and genomics
Anchor your data-handling answers in the syllabus techniques: PCR (why cycling is efficient but contamination-prone), gel electrophoresis for size separation, and Southern blotting with hybridisation probes for sequence confirmation.
Application prompt
Explain how lac operon control illustrates negative and positive regulation. Extend by predicting β-galactosidase expression when glucose is absent but lactose is present. [2]
Concept 3: Viral and bacterial genetics
Viruses: Lytic vs lysogenic cycles; describe integration as a prophage and triggers for induction. Account for variation in viral genomes, including antigenic drift and antigenic shift.
Bacteria: Conjugation (F plasmid pilus), transformation (uptake of naked DNA), transduction (phage-mediated). Each mechanism introduces genetic variation without sexual reproduction-ideal comparison to meiosis essays.
Worked scenario
Given colony growth on antibiotic media, decide whether resistance is more consistent with a chromosomal mutation or a horizontally transferred plasmid. Use evidence such as conjugation/transformation context, whether plasmids are present, and how quickly resistance appears across multiple isolates. [2]
Concept 4: Mutation, cancer, and genomics
Gene mutations: Point mutations (missense, nonsense, silent), insertion/deletion (frameshift). Use sickle cell anaemia (Glu6Val in the β-globin chain) as an example of a single substitution with major structure–function consequences. [2]
Chromosomal aberrations: Numerical (aneuploidy-trisomy 21 via nondisjunction) vs structural (translocation, inversion, duplication, deletion). Emphasise meiotic origin. [2]
Cancer genetics: Distinguish proto-oncogene activation (e.g. RAS pathway activation) vs tumour suppressor loss (e.g. p53). [2] Detail multistep models: accumulation of mutations and loss of checkpoint control that enables uncontrolled division. [2]
Meiosis: Reduction division; homologous chromosome pairing, crossing-over (chiasmata), independent assortment. Distinguish Meiosis I (reductional) vs Meiosis II (equational). Stress sources of variation: crossing-over, random assortment, random fertilisation.
Practical angle
Design a Paper 4 investigation to observe meiosis in onion anthers: staining (acetic orcein), squash preparation, stage identification, and data logging for PDO and ACE.
Monohybrid and dihybrid crosses: Use Punnett squares and probability trees, incorporating codominance (ABO blood groups) and incomplete dominance (snapdragon colour). [2]
Multiple alleles, epistasis, linkage: Work through dihybrid ratio deviations. Show how test crosses reveal linkage; map units approximate recombination frequency.
Sex linkage: X-linked recessive examples (haemophilia). Explain why males exhibit more frequently (hemizygous). [2]
Environmental influence: Honeybee caste differentiation via diet (e.g. royal jelly); human height (polygenic, environmental). [2]
Chi-squared practice
Adapted from the 9477/02 specimen paper: a self-pollinated maize plant produced 216 purple smooth, 78 purple shrunken, 65 yellow smooth, and 21 yellow shrunken grains (total 380). Test the observed phenotype counts against a 9:3:3:1 ratio: compute expected counts, calculate χ2, compare with the critical value at ν=3, and interpret whether you reject Mendelian segregation. [3]
Exam technique checkpoints
Paper 2: Practise interpreting pedigree charts and micrographs of cell division. Always state genotype with alleles (e.g. Rr) before phenotype.
Paper 3: Prepare essay outlines on “From mutation to cancer” and “Regulation of gene expression in eukaryotes vs prokaryotes.”
Paper 4: Run simulated chi-squared tests using yeast genetics or Drosophila crosses; justify sampling strategy, degrees of freedom, and use of null hypotheses.
Next in the series
Energy capture and utilisation builds on genetic instructions. Continue with Core Idea 3:
Energy and Equilibrium.
FAQ
Where can I find the full H2 Biology Notes series? Start at the H2 Biology Notes hub and move through Core Ideas 1–4 before the extension topics.
Where can I download a PDF of these Core Idea 2 notes? Use the “Download PDF” button on this page, or open the direct PDF link:
H2 Biology Core Idea 2 notes PDF.
