Natural selection and genetic modification

• Evolution


  A gradual change in the inherited traits within a population over time
• Evolution

  • Occurs due to natural selection
• Theory of natural selection

  1. Genetic variation exists due to spontaneous mutations

  2. Selection pressures (e.g. competition, disease) exist

  3. Random mutation gives an organism a selective advantage

  4. Organism is better adapted to the environment and survives

  5. Organism reproduces, passing on its beneficial alleles

  6. Frequency of advantageous alleles increase
• Competition between organisms in a habitat

  The resources within a habitat required for survival are limited
• Competition between organisms within a habitat

  • Competition between animals for food, shelter, mates etc.
  • Competition between plants for light, water, minerals etc.
• Antibiotic resistance in bacteria as an example of evolution

  1. Genetic variation exists due to spontaneous mutations

  2. Antibiotics act as a selection pressure

  3. Mutations gives a bacterium antibiotic-resistance

  4. If an antibiotic is administered, the bacterium is better adapted and survives, whilst other bacteria are killed

  5. Bacterium reproduces, passing on its resistant variant

  6. Frequency of antibiotic-resistant allele increases
• Antibiotic resistance in bacteria as a study for evolution

  Bacteria reproduce very rapidly, allowing the first-hand observation of evolution
• Fossils as evidence for evolution

  • Older fossils (found in rocks deeper in the ground) contain simpler organisms. Newer fossils (found closer to the surface) contain more complex organisms. Comparisons of fossils show that simple organisms evolved into more complex life forms.
  • Fossils can be organised into chronological order, allowing the changes in organisms over time to be observed
• Darwin's role in the development of the theory of evolution by natural selection

  • Studied a variety of organisms whilst travelling around the world on the HMS beagle
  • Noted that traits can be passed from parents to offspring
  • Proposed the idea of 'survival of the fittest'
  • Established the theory of natural selection and published his ideas in 'On the Origin of Species'
• Wallace's role in the development of the theory of evolution by natural selection

  • He proposed a theory of natural selection that was similar to Darwin's, although the mechanisms were different
  • He gathered greater evidence (e.g. studying warning colouration in butterflies) to support the theory
• Impact of the theory of evolution by natural selection

  • Enables the classification of organisms into taxa
  • Influences modern medicine by emphasising the importance of finishing antibiotic treatments and the need for the constant production of new antibiotics
  • Highlights the importance of high genetic diversity in habitats which aids conservation projects
• Classification


  The organisation of organisms into groups
• Taxonomy


  The classification of organisms into taxa: kingdom, phylum, class, order, family, genus, species
• Fossils that provided evidence for human evolution

  • 'Ardi' - 4.4 million years old
  • 'Lucy' - 3.2 million years old
  • Leakey discovered 1.6 million year old fossils
• Five kingdoms

  • Animals
  • Plants
  • Fungi
  • Protists
  • Prokaryotes
• As you move down the hierarchy of taxa

  The number of organisms in each taxon group decreases
• 'Ardi' fossil


  • Female hominid fossil. She shows phenotypic traits which encompass characteristics of both humans and apes:
  • Ape-like characteristics e.g. long arms, large big toes
  • Human-like characteristics e.g. the structure of her bones suggests that she walked upright
• Traditionally, organisms were grouped based on similarities and differences in their anatomy and behaviour
• Organisms that are not closely related may look alike and behave similarly if they live in the same environment e.g. sharks and dolphins
• 'Lucy' fossil

  • Female hominid fossil. She shows phenotypic traits which are more human-like than that of 'Ardi':
  • The structure of bones in her legs and feet are more adapted to walking than climbing
  • However, her brain size is closer to that of an ape's
• Some closely related species may look very different if they live in different habitats e.g. queen ants, worker ants
• Leakey's findings

  • He discovered many hominid fossils.
  • The 1.6 million year old fossil 'Turkana Boy' showed traits comparable to that of modern-day humans e.g. similar brain size.
• Advancements in science that have led to reconsidering the five kingdoms classification system

  • Microscopes
  • Biochemistry
  • DNA and RNA analysis
• Development of stone tools as evidence for evolution

  • Correlation between the development of more complex tools and an increase in brain size
  • Primitive tools are older than more complex tools. Brain size has increased over time ∴ as brain size increased, advancements in tool use were made.
• Three domains system of classification

  Organisms are initially divided into three groups: Archaea, Bacteria, Eukarya. Then kingdom, phylum, class, order, family, genus, species.
• Eukaryotic organisms belong to the domain Eukarya
• Prokaryotic organisms belong to the domains Archaea and Bacteria
• Methods used by scientists to date tools

  1. Carbon-14 dating - estimating the age of carbon-containing material that is found in tools (e.g. wooden handles) or alongside tools (e.g. fur)

  2. Stratigraphy - using the age of the layers of sediment surrounding the tool as an indication of the age of the tool
• Domain Bacteria


  Consists of true bacteria e.g. E.coli
• Domain Archaea


  Consists of primitive microorganisms, contains extremophiles - adapted to live in extreme conditions e.g. hot springs
• Pentadactyl limb


  A limb with five digits present in animals, bird, reptiles and amphibians
• Pentadactyl limb as evidence for evolution

  • The presence of the pentadactyl limb suggests that all species which possess it have descended from a common ancestor.
• Selective breeding


  The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes
• Selective breeding

  1. Identify a desired characteristic

  2. Select parent organisms that show the desired traits and breed them together

  3. Select offspring with the desired traits and breed them together

  4. Process repeated until all offspring have the desired traits
• Advantage of selective breeding

  • Creates organisms with desirable features: Crops produce a higher yield of grain, Cows produce a greater supply of milk, Plants produce larger fruit, Domesticated animals
• Other uses of selective breeding

  • In medical research
  • In sports e.g. horse racing
• Disadvantages of selective breeding

  • Reduction in the gene pool (which becomes especially harmful if sudden environmental change occurs)
  • Inbreeding results in genetic disorders
  • Development of other physical problems e.g. respiratory problems in bulldogs
  • Potential to unknowingly select harmful recessive alleles
• Plant cloning


  • Taking plant cuttings
  • Tissue culture
• Tissue culture


  A method of growing living tissue in a suitable medium
• Growing plants using tissue culture

  1. Select a plant that shows desired characteristics

  2. Cut multiple small sample pieces from meristem tissue

  3. Grow in a petri dish containing growth medium

  4. Transfer to compost for further growth