IGCSE›Cambridge IGCSE Biology›Mind mapsVariationCambridge IGCSE Biology: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat is it?Differences between individuals of a speciesRaw material for natural selectionFocus on within-species variationContinuousRange of phenotypes between two extremesMany intermediates, no clear categoriesGenes and environmentShown as a bell curvee.g. height, mass, skin colourDiscontinuousFew distinct phenotypes, no intermediatesCaused by genes onlyShown as a bar charte.g. blood groups, pea seed shapeVariationdifferences in a speciesMutationRandom change in DNA base sequenceCreates new allelesIonising radiation increases rateSome chemicals increase rateOther sourcesMeiosis: crossing over, independent assortmentRandom mating combines alleles unpredictablyRandom fertilisation: any sperm, any eggExam tipsDiscontinuous is not environmental onlyName all four sources of variationMutation creates; the rest recombine