natural selection & genetic modification

• Evolution


  The slow and continuous change of organisms from one generation to the next
• Natural Selection


  Survival of the fittest - come up with by Charles Darwin to explain how evolution occurs
• Natural Selection

  1. Individuals in a population show genetic variation

  2. Selection pressures affect an organism's chance of surviving and reproducing

  3. Individuals with beneficial characteristics are more likely to survive and reproduce

  4. Beneficial characteristics become more common in the population over time

  5. Less well adapted individuals are less likely to survive and reproduce
• Evidence for evolution

  • Antibiotic resistance in bacteria
  • Emergence of other resistant organisms (e.g. rats resistant to warfarin)
• Fossils


  • Trace of an animal or plant that lived a long time ago (over a thousand years)
  • Found in rocks, with older fossils in deeper rock layers
  • Provide evidence for evolution by showing gradual changes in organisms over billions of years
• Fossil evidence for human evolution

  • Ardipithecus ramidus (Ardi 4.4 million years old)
  • Australopithecus afarensis (Lucy, 3.2 million years old)
  • Leakey’s discovery of fossils from 1.6 million years ago
• Fossil evidence for human evolution

  • Arms and leg length shorter over time, brain size increases over time
  • Shows gradual changes in characteristics over time, with more human-like features in later fossils
• Stone tool development

  1. Homo habilis made simple pebble tools

  2. Homo erectus made more complex hand-axes

  3. Homo neanderthalensis made even more complex tools including flint and wooden spears

  4. Homo sapiens made a wide variety of advanced tools including arrowheads, fish hooks and needles
• Dating methods for fossils and tools

  • Structural features (simpler tools are older)
  • Stratigraphy (older rock layers are below younger layers)
  • Carbon-14 dating of associated organic material
• Classification

  Organising living organisms into groups based on similarities and differences in observable characteristics
• Five kingdom classification system

  • Animals
  • Plants
  • Fungi
  • Prokaryotes
  • Protists
• Classification systems change over time as technology and understanding improves
• Comparing DNA sequences is now used to determine evolutionary relationships between organisms
• Kingdoms

  • Animals
  • Plants
  • Fungi
  • Prokaryotes
  • Protists
• Kingdom are subdivided into smaller groups that have commen featuresKingdom

  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Classification systems change over time
• The five kingdom classification system is still used, but it's now a bit out of date
• Technology has developed further and our understanding of things like biochemical processes and genetics has increased. This led to a rethink about the way organisms are classified and to the proposal of the three domain system of classification by a scientist called Carl Woese
• We are now able to determine the sequence of DNA bases in different organisms' genes and compare them
• The more similar the sequence of a gene, the more closely related the organisms
• The three domains

  • Archaea
  • Bacteria
  • Eukarya
• Archaea

  Organisms in this domain look similar to bacteria but are actually quite different, as differences in their genetic sequences show. They were first found in extreme places such as hot springs and salt lakes.
• Bacteria

  This domain contains true bacteria like E. coli and Staphylococcus.
• Eukarya

  This domain includes a broad range of organisms including fungi, plants, animals and protists.
• The three domains are then subdivided into smaller groups used in the five kingdom system (beginning with kingdom and finishing with species - kingdom, phylum, class, order, family, genus, species).
• Selective breeding


  Artificially selecting the plants or animals that are going to breed so that the genes for particular characteristics remain in the population.
• Selective breeding process

  1. Select from your existing stock the ones which have the characteristics you're after

  2. Breed them with each other

  3. Select the best of the offspring, and breed them together

  4. Continue this process over several generations, and the desirable trait gets stronger and stronger
• Selective breeding is nothing new - people have been doing it for thousands of years. It's how we ended up with edible crops from wild plants and how we got domesticated animals like cows and dogs.
• Advantages of selective breeding

  • Improve meat yields in cattle
  • Crops with disease resistance
  • Dogs with a good, gentle temperament
  • Plants that produce bigger fuit
  • Investigate reasons behind alcoholism in rats
• Disadvantages of selective breeding

  • Reduces the gene pool - the number of different alleles (forms of a gene) in a population
  • Increases risk of inheriting harmful genetic defects when the gene pool is limited
  • Reduces resistance to new diseases
• Genetic engineering

  Modifying an organism's genome (DNA) to introduce desirable characteristics
• Genetic engineering process

  1. Use restriction enzymes to cut DNA at specific sequences - piece of DNA left with sticky ends where cut

  2. Use ligase enzymes to join pieces of DNA together at their sticky ends

  3. Two different bits of DNA stuck together are known as recombinant DNA
• Uses of genetic engineering

  • Make crops resistant to herbicides
  • Produce human proteins in animals for medical use
• There are concerns about the genetic engineering of animals and crops, as it can be hard to predict what effects there will be on the organism and transplanted genes may get out into the environment