Natural selection & Genetic modification

• Wallace: developed the theory of speciation

  • geographical barriers can separate a population of a species, preventing inbreeding
  • different alleles are useful in different environments and are selected for through natural selection
  • over time, genetic variation increases between populations so they can no longer breed - a new species is produced
• Darwin: developed the theory of evolution

  • variation exists within a population
  • characteristics more suited to the environment survive through natural selection, and reproduce
  • useful characteristics are passed unto generations
• Resistance:

  • bacteria reproduce at a fast rate - mutations can result in the gene for antibiotic resistance (creation of a new strain)
  • this creates a selection pressure, so the population of antibiotic-resistant bacteria increases - proving Darwin's theory of natural selection
• Fossil evidence for human evolution:

  • Ardi is a fossilised skeleton from 4.4 million years ago that contains humanoid features but also resembles an ape
  • Lucy is a fossilised skeleton from 3.2 million years ago that suggests she walked in a human upright position, however, had a small chimpanzee skull
• Stone tool evidence for human evolution:

  • homo habili used basic pebble tools
  • homo neanderthals and homo sapiens used pointed arrowheads and spears
  • these can be dated using radiometric carbon dating, looking at the natural radioactive decay of carbon, or by stratifying rock layers, looking at the layers of sediment where it was found
• Pentadactyl limb:

  • a limb with five digits can be seen in a number of organisms
  • this suggests that organisms have a common ancestor, who also had a similar bone structure
  • organisms have evolved to carry out different functions
• Classification:

  • kingdom, phylum, class, order, family, genus, species
  • the five kingdoms are animals, plants, fungi, prokaryotes (bacteria), protists (algae, amoebas)
  • the binomial name system is based on the genus and species
  • the three-domain system based on improvement of the microscope sorted these into archaea, bacteria, and eukaryota
• Selective breeding:

  • parents with desired characteristics chosen and bred. Offspring with the desired characteristics chosen and bred - this is repeated many times
  • a problem is inbreeding leading to genetic defects, and disease spreading easily due to the small gene pool
• Tissue culture:

  • remove a piece of tissue from the root or shoot tip of a plant using sterile tweezers, place the tissue on a growth medium (containing hormones and nutrients), once the tissue has developed, it can be transferred to compost to grow
  • produces lots of offspring with desirable features and increases yield
  • disease can spread easily, can lead to genetic problems
• Genetic engineering: modifying the genome of an organism to introduce desirable characteristics

  • genes from human chromosome cut using restriction enzymes, the same restriction enzymes cut bacterial plasmid
  • ligase is used to attatch sticky ends of the gene and plasmid together to produce a recombinant gene product
  • the vector is placed in an organism to grow
• Genetically modified organisms (GMO):

  • GM crops are engineered to be resistant to insects and herbicides, which increases yield as less crops die, however it creates a selection pressure and reduces biodiversity
  • GM in medicine can cure inherited disorders using gene therapy, which involves transferring normal genes into patients to correct the proteins produced
  • Bacillus thuringiensis is the bacteria that kills insect larvae - its genes are used in crops to stop insects from eating it
• Agricultural solutions: helps with the demands of the growing human population

  • fertilisers provide nutrients to plants and makes them grow faster, however they can run into rivers and cause eutrophication
  • biological control is the use of certain species to control the population of another species, however it reduces biodiversity