Biology Module 6 Overview

Overview

This lecture covers the full OCR A-Level Biology Module 6, focusing on cellular control, inheritance, manipulating genomes, biotechnology, ecosystems, and populations, with key examples, definitions, and processes relevant to the exam.

Cellular Control & Gene Mutations

• Gene mutations are changes in DNA base sequence, occurring randomly during DNA replication (S phase).
• Mutagenic agents (e.g., UV light, ionizing radiation, carcinogens) increase mutation rates.
• Types of mutations: substitution (may be silent due to genetic code degeneracy), deletion, and insertion (both cause frameshifts).
• Mutations may change amino acid sequence, protein folding, and function; effects can be harmful, beneficial, or neutral.
• Transcription factors control gene expression by binding DNA and initiating or inhibiting transcription.
• The Lac operon in prokaryotes is a model for gene regulation, responding to lactose presence and involving repressors and cyclic AMP.

Genetic Control of Development

• Homeobox and Hox genes regulate body plan development in embryos; gene order matches expression order.
• Mitosis increases cell number; apoptosis removes unnecessary cells; both are tightly gene-regulated.
• Tumor suppressor genes inhibit, and proto-oncogenes stimulate the cell cycle.

Inheritance & Genetic Crosses

• Monohybrid, codominant, multiple allele, sex-linked, dihybrid, and autosomal linkage inheritance patterns require specific genetic diagrams.
• Epistasis occurs when one gene masks the expression of another.
• Dihybrid crosses typically show a 9:3:3:1 ratio unless linkage or epistasis intervene.
• Crossing over and autosomal linkage affect phenotype ratios.
• The chi-squared test analyzes if observed genetic ratios match expected ones.
• Hardy-Weinberg equations predict allele and genotype frequencies in populations.

Variation, Selection & Speciation

• Continuous variation is quantitative (e.g., height); discontinuous is categorical (e.g., blood group).
• Selection types: directional (favors extremes), stabilizing (favors mean), disruptive (favors both extremes).
• Speciation: allopatric (geographical isolation), sympatric (reproductive isolation within same area).
• Genetic drift, bottlenecks, and founder effect reduce genetic diversity, especially in small populations.
• Artificial selection (e.g., breeding dogs/plants) contrasts with natural selection.

Manipulating Genomes & Genetic Engineering

• Genome sequencing allows disease screening and species comparison; high-throughput techniques have sped up the process.
• DNA profiling uses variable number tandem repeats (VNTRs) and gel electrophoresis.
• PCR amplifies DNA using primers and thermostable polymerase.
• Genetic engineering uses restriction enzymes, plasmids, and marker genes to insert desired DNA into organisms.
• Transgenic plants/animals/microorganisms are used for higher yields, resistance, or medicine production.
• Gene therapy: somatic (body cells, not inherited) vs germline (gametes, inherited), with somatic being temporary.
• Cloning: natural (runners, identical twins), artificial (embryo splitting, somatic cell nuclear transfer).

Biotechnology & Microorganisms

• Microorganisms are used in food production (bread, cheese, yogurt, mycoprotein), medicine, and environmental cleanup (bioremediation).
• Batch vs continuous fermentation techniques optimize microbial growth and product yield.
• Microbial growth follows lag, exponential, stationary, and death phases; population size is calculated using n = n₀ × 2ⁿ.
• Immobilized enzymes offer specificity and efficiency in biotechnology applications.

Ecosystems, Cycles & Succession

• Ecosystems are dynamic, comprising biotic and abiotic factors; energy transfer between trophic levels is inefficient.
• Nitrogen and carbon cycles rely on specific bacteria for nutrient transformation.
• Succession describes changes in species composition over time, from pioneer to climax communities; human activity can cause deflected succession.

Population & Sustainability

• Abiotic and biotic factors influence population size; predator-prey relationships show cyclical trends.
• Conservation increases biodiversity; preservation protects areas by limiting access.
• Sustainable management (e.g., forestry, fishing) balances resource use and environmental health.

Key Terms & Definitions

• Gene mutation — change in base sequence of DNA.
• Transcription factor — protein that initiates or inhibits transcription.
• Operon — group of genes under common control, typically in bacteria.
• Homeobox gene — gene that regulates body plan development.
• Epistasis — one gene affects expression of another gene.
• Hardy-Weinberg equilibrium — mathematical model for allele/genotype frequencies.
• Genetic drift — change in allele frequency due to random sampling.
• Bioremediation — use of organisms to break down pollutants.
• Chi-squared test — statistical test to compare observed and expected frequencies.

Action Items / Next Steps

• Create and review flashcards for key terms, definitions, and cycle stages.
• Practice drawing genetic crosses (Punnett squares) for different inheritance patterns.
• Memorize the steps and key enzymes involved in PCR, genetic engineering, and DNA profiling.
• Review sample chi-squared calculations and Hardy-Weinberg problems.