Back to revision notes Open full-size SVG Print mind map CB3 · Overview Genetics mind map Use your browser’s Print command for A4 landscape, or choose A3 in its paper settings. The SVG remains sharp when enlarged. A text version follows the map.
Read the mind map as text Reproduction Gametes: Sperm and egg are haploid: 23 chromosomes in humansMeiosis: DNA copied; two divisions → four different haploid cellsFertilisation: Nuclei fuse: 23 + 23 → diploid zygote with 46Sex chromosomes: Standard model: XX female, XY male; eggs X, sperm X or YProbability: XX : XY = 1 : 1; each fertilisation independentDNA Nucleotides: Sugar + phosphate + base; base order stores informationDouble helix: Two strands; sugar–phosphate backbonesPairing: Hydrogen bonds: A–T and C–G; ATGC pairs with TACGGenes: Chromosomes: DNA; genes: protein instructionsAlleles: Different versions of a geneGenome: All DNA, including non-coding regionsDNA evidence Release: Crush; detergent breaks membranes; salt aids DNASeparate: Filter; cold ethanol precipitates dissolved DNAObserve safely: Visible strands: many molecules; flammable ethanolGenome project: Reference sequence from multiple people; identify genesApplications: Variants: diagnosis, risk and targeted medicineDecisions: Benefits versus privacy, consent and discriminationInheritance Genotype / phenotype: Alleles / traits; environment also affects traitsSymbols: AA or aa: homozygous; Aa: heterozygousDominance: AA / Aa dominant; aa recessive; Aa may carryLimits: Dominant ≠ common / better; many traits polygenicPedigrees: Square: male; circle: female; shading: use keyInference: Recessive affected: aa; retain genotype uncertaintyPunnett squares Method: Write parental gametes; combine alleles in each boxAa × Aa: AA, Aa, Aa, aa; genotype 1 : 2 : 1Phenotype: Complete dominance: 3 : 1; recessive probability 25%Other crosses: Aa × aa → 1 : 1; AA × aa → all AaChance: Independent chance; proportions not guaranteedExpected number: Probability × total; 0.25 × 80 = 20Variation Sources: Genetic, environmental or both; height involves bothNew combinations: Meiosis and fertilisation reshuffle existing allelesMutations: DNA changes; errors or mutagens; effects varyAcquired traits: Scars / diet do not usually alter inherited allelesData types: Continuous: height; discrete categories: ABOGraphs: Histograms: intervals; bars: categories; shapes varyConnections DNA → Inheritance: Alleles are gene variants passed to offspring. Reproduction → Variation: Meiosis and random fertilisation create combinations. 