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'
• 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
• 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
• 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
• Impact of the theory of evolution by natural selection on modern biology and society

  • 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
• Other uses of selective breeding


  • In medical research
  • In sports e.g. horse racing
• 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
• '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
• 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
• Cloning plants


  1. Taking plant cuttings

  2. Tissue culture
• '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
• 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.
• Tissue culture


  A method of growing living tissue in a suitable medium
• 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.
• 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
• 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
• Ensure aseptic conditions to prevent contamination by microorganisms when preparing tissue cultures
• Growth medium


  Contains nutrients and growth hormones
• Pentadactyl limb


  A limb with five digits present in animals, bird, reptiles and amphibians
• Selective breeding


  The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes
• Advantages of growing plants by tissue culture

  • Fast and simple process
  • Requires little space
  • Enables the growth of many plant clones with the same desirable characteristics
  • Useful in the preservation of endangered plant species
• 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


  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
• Disadvantages of growing plants by tissue culture

  • Reduction in the gene pool
  • Plant clones often have a low survival rate
  • Could unknowingly increase the presence of harmful recessive alleles
• 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
• Animal tissue culturing


  Useful in the preparation of tissue samples for medical research, Enables the investigation of how different factors may affect a specific animal tissue, without harming the animal itself
• Other uses of selective breeding


  • In medical research
  • In sports e.g. horse racing
• Preparing animal tissue cultures

  1. Extract a sample of tissue from an animal

  2. Use enzymes to separate cells within the sample

  3. Grow in a culture vessel containing growth medium

  4. Once grown, store the sample
• 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
• Genetic engineering


  The modification of the genome of an organism by the insertion of a desired gene from another organism, Enables the formation of an organism with beneficial characteristics
• Plant cloning


  • Taking plant cuttings
  • Tissue culture