explain the terms gene, locus, allele, dominant, recessive, codominant, linkage, test cross, F1, F2, phenotype, genotype, homozygous and heterozygous

Topic 1 – Cell Structure

• Prokaryotic vs eukaryotic cells – size, nucleus, organelles.
• Key organelles: nucleus (DNA storage), mitochondria (ATP), chloroplasts (photosynthesis), endoplasmic reticulum (protein/lipid synthesis), Golgi apparatus (modification & sorting), lysosomes (digestion), vacuoles (storage), cytoskeleton (shape & transport).
• Plasma membrane structure – phospholipid bilayer, fluid‑mosaic model, integral & peripheral proteins.
• Cell wall in plants, fungi and bacteria – composition (cellulose, chitin, peptidoglycan) and function.

Topic 2 – Biological Molecules

• Carbohydrates – monosaccharides, disaccharides, polysaccharides; energy storage (starch, glycogen) and structural roles (cellulose).
• Proteins – amino‑acid structure, peptide bonds, levels of organisation, enzyme catalysis (active site, induced fit).
• Lipids – fatty acids, triglycerides, phospholipids, steroids; role in membranes and energy storage.
• Nucleic acids – DNA & RNA structure, nucleotides, base pairing.

Topic 3 – Enzymes

• Enzyme structure – protein catalyst, active site specificity.
• Factors affecting activity: temperature, pH, substrate concentration, enzyme concentration, inhibitors (competitive, non‑competitive).
• Enzyme kinetics – Michaelis‑Menten equation, Vmax, Km.
• Co‑enzymes & co‑factors (e.g., NAD⁺, metal ions).

Topic 4 – Cell Membranes & Transport

• Diffusion, osmosis, facilitated diffusion, active transport (primary & secondary).
• Transport proteins – channels, carriers, pumps.
• Bulk transport – endocytosis (phagocytosis, pinocytosis) and exocytosis.
• Membrane potential – ion gradients, Nernst equation, role in nerve impulse.

Topic 5 – Cell Cycle & Cell Division

• Phases of the mitotic cycle – G₁, S, G₂, M (prophase, metaphase, anaphase, telophase) and cytokinesis.
• Control mechanisms – cyclins, CDKs, checkpoints (G₁‑S, G₂‑M, spindle).
• Meiosis – two successive divisions (Meiosis I & II), reductional vs equational division, formation of haploid gametes.
• Key differences between mitosis and meiosis (chromosome number, genetic variation).

Topic 6 – Nucleic Acids & Protein Synthesis

DNA structure and replication

• Double helix; antiparallel strands; base pairing (A–T, G–C).
• Semi‑conservative replication – each daughter DNA contains one parental strand.
• Key enzymes: DNA helicase, DNA polymerase (5’→3’ synthesis), primase, ligase, topoisomerase.
• Telomeres protect chromosome ends; telomerase adds repeats in germ cells.

Transcription

• RNA polymerase synthesises a complementary mRNA strand from DNA template.
• In eukaryotes, primary transcript undergoes 5’ capping, poly‑A tail addition, and splicing to remove introns.

Translation

• mRNA codons (triplets) are read by ribosomes; tRNA delivers the appropriate amino acid.
• Polypeptide chain elongation, termination and post‑translational folding.

Topic 7 – Plant Transport

• Water movement – cohesion‑tension theory, root pressure, transpiration pull.
• Mineral transport – xylem (unidirectional, upward) and phloem (bidirectional, source to sink).
• Regulation of stomatal opening (guard cells, ABA, light).

Topic 8 – Animal Transport

• Circulatory system – heart structure, blood vessels, double circulation in mammals.
• Blood components – plasma, red & white cells, platelets; haemoglobin function.
• Exchange of gases and nutrients at capillaries; role of diffusion distance.

Topic 9 – Gas Exchange

• Respiratory surfaces – lungs (alveoli), gills, skin.
• Ventilation mechanisms – diaphragm, intercostal muscles, tidal volume.
• Partial pressure gradients drive O₂ uptake and CO₂ removal.

Topic 10 – Infectious Disease & Immunity

• Pathogen types – bacteria, viruses, fungi, protozoa; routes of transmission.
• Innate immunity – physical barriers, phagocytes, inflammation, fever.
• Adaptive immunity – B‑cell antibodies (humoral), T‑cell mediated response (cellular), memory cells, vaccination.
• Examples of immune disorders – allergies, autoimmune disease, immunodeficiency.

Topic 11 – Respiration

• Cellular respiration – glycolysis, link reaction, Krebs cycle, oxidative phosphorylation.
• ATP yield (≈ 38 ATP per glucose in prokaryotes, 30‑32 ATP in eukaryotes).
• Anaerobic pathways – lactic acid fermentation, alcoholic fermentation.
• Regulation of respiration – substrate availability, ADP concentration, feedback inhibition.

Topic 12 – Photosynthesis

• Overall equation: 6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂.
• Light‑dependent reactions – thylakoid membranes, photosystems II & I, water splitting, ATP & NADPH formation.
• Calvin cycle – CO₂ fixation (Rubisco), reduction, regeneration of RuBP.
• Factors affecting rate – light intensity, CO₂ concentration, temperature.

Topic 13 – Homeostasis

• Feedback mechanisms – negative (e.g., blood glucose regulation) and positive (e.g., oxytocin during labour).
• Control of temperature – sweating, shivering, vasodilation/vasoconstriction.
• Regulation of water balance – antidiuretic hormone (ADH), renal concentrating ability.

Topic 14 – Control (Nervous & Hormonal)

• Nervous system – neuron structure, action potential generation, synaptic transmission.
• Hormonal system – endocrine glands, hormone classification (peptide, steroid, amine), mechanisms of action.
• Interaction between nervous and endocrine systems (e.g., hypothalamic‑pituitary axis).

Topic 15 – Evolution

• Evidence for evolution – fossil record, comparative anatomy, molecular phylogeny.
• Natural selection – variation, differential survival/reproduction, inheritance.
• Speciation mechanisms – allopatric, sympatric, reproductive isolation.
• Genetic drift, gene flow, mutation as sources of variation.

Topic 16 – Inheritance (Genetics & Inheritance)

Glossary of Key Terms

Monohybrid Cross (Mendelian Inheritance)

Consider a single gene with alleles A (dominant) and a (recessive).

F₁ generation: All offspring are Aa (heterozygous) → dominant phenotype.

F₂ generation (Aa × Aa)

Genotypic ratio: 1 AA : 2 Aa : 1 aa

Phenotypic ratio (dominant : recessive): 3 : 1

Dihybrid Cross – Independent Assortment

Two unlinked genes: A/a and B/b.

Phenotypic ratio: 9 : 3 : 3 : 1 (dominant A & dominant B : dominant A & recessive b : recessive a & dominant B : recessive a & recessive b).

Sex‑Linked Inheritance (X‑linked)

Linkage & Genetic Mapping

• Genes on the same chromosome are linked; recombination occurs only if crossing‑over separates them.
• Parental (non‑recombinant) gametes retain the original allele combinations; recombinant gametes arise from crossing‑over.
• Recombination frequency (θ) estimates map distance: 1 % θ ≈ 1 cM.

Example – Genes A and B are linked. Parental gametes: AB and ab. After crossing‑over, recombinant gametes Ab and aB appear at 10 % frequency.

Test Cross

1. Cross the individual of unknown genotype with a homozygous recessive (aa).
2. Interpret the offspring:

   • All dominant phenotype → unknown is AA (homozygous).
   • 1 : 1 ratio of dominant : recessive → unknown is Aa (heterozygous).

Non‑Mendelian Interactions

• Incomplete dominance – heterozygote phenotype intermediate (e.g., snapdragon flower colour).
• Codominance – both alleles expressed (e.g., ABO blood group I^AI^B = AB).
• Epistasis – one gene masks the effect of another.

  • Example: In pea plants, gene A (flower colour) is epistatic to gene B (pigment production). AA bb plants are white because bb prevents pigment formation, giving a phenotypic ratio of 9 : 3 : 4 (purple : red : white).

• Polygenic inheritance – many genes each contribute a small effect, producing a continuous distribution (e.g., human skin colour, height).

Pedigree Analysis (AO3)

• Standard symbols: squares (male), circles (female), filled = affected, half‑filled = carrier (for recessive X‑linked).
• Steps:

  1. Identify mode of inheritance (autosomal dominant, autosomal recessive, X‑linked dominant/recessive).
  2. Determine if the trait appears in every generation (dominant) or skips generations (recessive).
  3. Check sex distribution for X‑linked patterns.
  4. Calculate probability of a particular genotype for a given individual using the pedigree.

Sample Calculation – Recombination Frequency

In a test cross involving linked genes A and B, 200 offspring are produced. 30 are recombinant (Ab or aB).

θ = (30 ÷ 200) × 100 % = 15 % → map distance ≈ 15 cM.

Summary Checklist for Genetics Questions

• Identify locus, alleles and their interaction (dominant, recessive, codominant, incomplete).
• Draw correct Punnett squares for monohybrid, dihybrid, sex‑linked and linked‑gene crosses.
• State expected F₁ and F₂ genotypic and phenotypic ratios.
• Use a test cross to determine hidden heterozygosity.
• Calculate recombination frequency and convert to centimorgans.
• Analyse pedigrees to deduce inheritance pattern and genotype probabilities.
• Explain epistasis, polygenic inheritance and the effect of mutations on phenotype.
• Recall the steps of DNA → RNA → protein and the key molecular techniques (PCR, gel electrophoresis, DNA sequencing, CRISPR‑Cas9).

Suggested Diagrams (to be drawn by the learner)

• Punnett square for a monohybrid cross (AA × aa) and the corresponding test cross (Aa × aa).
• Dihybrid cross showing the 9 : 3 : 3 : 1 phenotypic ratio.
• Linkage diagram with parental and recombinant gametes, indicating map distance.
• Schematic of DNA → RNA → Protein (including transcription and translation steps).
• Pedigree for an autosomal recessive disorder and one for an X‑linked trait.

Topic 17 – Genetic Technology

• Recombinant DNA – cutting DNA with restriction enzymes, ligating into plasmids, transformation of bacteria.
• Polymerase Chain Reaction (PCR) – denaturation, annealing of primers, extension by Taq polymerase; exponential amplification of a target fragment.
• Gel electrophoresis – separation of DNA fragments by size; visualization with ethidium bromide or safe dyes.
• DNA sequencing – Sanger method (chain‑termination) and next‑generation sequencing (NGS) basics.
• CRISPR‑Cas9 – guide RNA directs Cas9 to a specific DNA sequence; double‑strand break repaired by non‑homologous end‑joining (knock‑out) or homology‑directed repair (knock‑in).
• Applications: gene therapy, genetically modified crops, forensic DNA profiling, disease diagnostics.

Topic 18 – Evolution (Advanced)

• Population genetics – Hardy‑Weinberg equilibrium, factors causing deviation (selection, mutation, migration, drift).
• Phylogenetic trees – construction using morphological and molecular data; interpretation of branch lengths and common ancestors.
• Speciation mechanisms revisited – reinforcement, hybrid zones, polyploidy in plants.

Topic 19 – Biodiversity & Conservation

• Classification hierarchy – domain, kingdom, phylum, class, order, family, genus, species.
• Conservation strategies – protected areas, captive breeding, genetic rescue, legislation (CITES).
• Impact of human activities – habitat loss, invasive species, climate change, over‑exploitation.
• Role of biodiversity in ecosystem stability and services.