B6 - Inheritance, Variation & Evolution

  • Created by: Benny52
  • Created on: 21-01-19 17:39


  • Charles Darwin - evolution by natural selection. Concluded organisms with most suitable characteristics for environment would be more successful competitiors & more likely to survive - survival of the fittest. Successful organisms that survive more likely to reproduce & pass on genes for characteristics that made them successful to offspring. Over time, beneficial characteristics become more common in population & species changes - evolves.
  • Theory wasn't perfect as relevant scientific knowledge wasn't available at time, so couldn't give good explanation for why new characteristics appeared or how individual organisms passed on beneficial adaptations.
  • Discovery of genetics supported his idea - provided explanation of how organisms born with beneficial characteristics can pass them on and showed it's genetic variants that give rise to phenotypes suited to environment. Other evidence found by looking at fossil record - allows you to see how changes in organisms developed slowly over time. Discovery of how bacteria are able to evolve to become resistant to antibiotics supports evolution by natural selection.
  • Over long period of time, phenotype of organisms can change so much due to natural selection that a new species is formed - speciation. Happens when populations of same species change enough to become reproductively isolated - they can't interbreed to produce fertile offspring.
  • Extinction - When no individuals of a species remain. Species become extinct because: Environment changes too quickly, New predator kills them, New disease kills them, Can't compete with another species for food, Catastrophic event happens that kills them.
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Antibiotic-Resistant Bacteria

  • Bacteria sometimes develop random mutations in DNA - leads to changes in bacteria's characteristics, e.g. being less affected by a particular antibiotc. Leads to antibiotic-resistant strains forming as gene for antibiotic resistance becomes more common in population. Can evolve quickly - bacteria reproduces rapidly. Bacteria able to survive better - reproduces - increases population size of strain.
  • Problem for people who become infected with bacteria as they aren't immune to new strain and there's no effective treatment - easily spreads. 'Superbugs', resistant to most known antibiotics becoming more common - MRSA - affects people in hospital and can be fatal if it enters blood.
  • Problem of antibiotic resistance getting worse, partly due to overuse and inappropriate use of antibiotics. Important that doctors only prescribe antibiotics when they really need to - antibiotics don't cause resistance - they create situation where naturally resistant bacteria have advantage so they increase in no. Also important to take all antibiotics docter prescribes - ensures all bacteria are destroyed, so there's none left to mutate & develop into antibiotic-resistant strains.
  • Farming - antibiotics given to animals to prevent them from getting ill & to make them grow faster. Leads to development of antibiotic-resistant bacteria which can spread to humans.
  • Increase in antibiotic resistance encouraged drug companies to work on developing antibiotics effective against the resistant strains. Rate of development is slow, meaning we're unlikely to be able to keep up with the demand for new drugs as more antibiotic-resistant strains develop & spread. Also very costly process.
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  • Traditionally, organisms classified according to system proposed in 1700s by Carl Linnaeus - groups living things according to characteristics and structures that make them up. Linnaean system - living things first divided into kingdoms (animal, plant). Then subdivided into smaller and smaller groups - phylum, class, order, family, genus, species.
  • As knowledge of biochemical processes taking placed inside organisms developed and microscopes improved - allowing us to find out more about the internal structures of organisms - scientists put forward new models of classifiaction. 1990 - Carl Woese - three-domain system. Using evidence from new chemical analysis techniques, he found in some cases, species thought to be closely related in traditional classification systems are not as closely related. DomainsArchaea - primitive bacteria. Often found in exteme placesBacteria - true bacteria. Often look similar to Archaea but lots of biochemical differencesEukaryota - includes broad range of organisms - fungi, plants, animals & protistsThese are then subdivided into smaller groups: kingdom, phylum...
  • Binominal system - every organism given its own 2-part latin name. First part refers to genus - gives information on organism's ancestry. Second part - species.
  • Evolutionary trees show how scientists think different species are related to each other. Show common ancestors & relationships between species. The more recent the common ancestor, the more closely related the two species, and the more likely shared characteristics. Scientists analyse lots of different types of data to work out evolutionary relationships. Living organisms - current classification data. Extinct species - fossil record.
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