Variation and selection
Variation
- VariationDifferences within a species
- ContinuousRange between extremesBody length, massGenes and environment
- DiscontinuousNo intermediatesABO blood groupsPea seed shape, colourGenes only
- MutationGenetic changeNew alleles
- Increase mutation rateIonising radiationSome chemicals
- Gene mutationSupplementRandom change in base sequence
- Sources of variationSupplementMutationMeiosisRandom matingRandom fertilisation
Adaptive features
- Adaptive featureInheritedHelps survive and reproduce
- Polar bearWhite fur camouflageFat insulation
- CactusSpinesThick stem stores water
- HydrophytesSupplementAir spacesStomata on upper surface
- XerophytesSupplementThick waxy cuticleReduced leaf areaWater storage
Selection
- Natural selectionVariationMany offspringStruggle for survivalAlleles passed on
- AdaptationSupplementPopulation more suited over generations
- Antibiotic resistanceSupplementMutationResistant surviveAllele passed on
- Selective breedingSelectCrossSelect offspringMany generations
- Natural vs artificialSupplementEnvironment selectsHumans select