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B1b 7 Evolution

B1b 7 Evolution. 7.3 Natural selection. Learning objectives. Understand how natural selection works Know what a mutation is Understand what is involved in extinction. The Peppered Moth. Natural Selection. Organisms gain an advantage in competition Against other species

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B1b 7 Evolution

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  1. B1b 7 Evolution 7.3 Natural selection

  2. Learning objectives • Understand how natural selection works • Know what a mutation is • Understand what is involved in extinction

  3. The Peppered Moth

  4. Natural Selection • Organisms gain an advantage in competition • Against other species • Against own species • More likely to thrive, survive and breed • Nature has selected the individual

  5. Survival of the fittest • Animal always produce too many offspring • They don’t all survive • Individuals in a species show variation • Due to genes - DNA • Those with best suited genes • Breed, feed, stay alive • Think about bunnies – what gets passed on and what doesn’t

  6. Mutants • Natural mistakes when DNA is being copied • Happens when cells divide • New form of a gene (allele) • Might have no effect • Gene might do something different • Introduces variety into the species • Increases survival of species

  7. Bacteria Penicillin Evolution in action • Antibiotic resistant bacteria • Variation – some strains resistant, some aren’t • Competition – non-resistant bacteria killed by penicillin. • Survival of the fittest – resistant bacteria survive • Passing on of genes – resistant bacteria reproduce - pass on adaptations to offspring

  8. Extinction • Millions of species exist today, but billions have existed • Extinct • Changing conditions • Organisms adapt to survive – new food, habitat • Organisms that don’t adapt – die out • Extinction is essential to balance number of species

  9. Environmental change • Animals adapted to one extreme won’t survive in another • Main cause of extinctions • Dinosaurs - perfectly adapted • sudden change in climate • Too cold • Mammals could survive

  10. Top 5 extinction events • 500 million years ago – trilobites • 430 million years ago – plants and fish • 350 million years ago – 70% all species • 225 million years ago – amphibians and invertebrates • 65 million years ago – dinosaurs • Next year – humans?

  11. Causes of extinction • New diseases – organisms have developed immune response – swine flu • New predators – Tibbles the cat • New competitors – species replacement • Famous case – The Dodo

  12. Learning outcomes • How does natural selection work? • What is a mutation and what effect can it have? • What might be involved in an extinction?

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