Topic 4: Natural Selection

• Evolution - a gradual change in the characteristics of a species over time
• Binomial species names are based off classifications such as dogs (cannis familiaris) and humans (homo sapiens) where the genus comes before the species
• Evidence for human evolution usually comes from fossils and stone tools
• Stone Tools:

  • more prominent shapes in earth levels which match increasing intelligence (advantage)
  • dates of sediment aren't accurate (disadvantage)
  • tools are rare and easily damaged as specific conditions such as geological activity are required (disadvantage)
  • sub-species that went extinct could've also used stone tools for millions of years (e.g. current apes)
• Fossils Advantage:

  • suspected ancient human skeletons showed bone changes for body structure and increasing skull size
  • Ardi 4.4 million years ago had a mixture of humans and apes like bone structures for walking upright and climbing trees
  • Lucy 3.2 million years ago is more human-like and had a larger skull and arched feet for walking
  • Leakey discovered the Turkana Boy skeleton that was 1.6 million years old had even more human-like than Lucy with short arms and long legs
• Fossil Disadvantage:

  • gaps/jumps in characteristics show scientists can't be certain from fossil records as theoretically the transition should be smoother
• Genetic variation is caused by mutations which causes creatures to become more adapted to survive their environment so they survive longer and reproduce more.

  This natural selection means the advantageous alleles are passed to offspring which leads to evolution
• Darwin observed the Galapagos finches and concluded with his theory of evolution. Evolution of resistance in bacteria is an example of natural selection and supports this theory.
• Development of Bacterial Resistance:

  1. Random mutation occurs in genes of individual bacteria cells
  2. Some mutations protect bacterial cell from antibiotic effects
  3. Bacteria without mutation die and cannot reproduce with antibiotic present
  4. Surviving bacteria reproduce and second generation is more resistant to antibiotics
• Penicillin (first antibiotic mass produced in 1940s) has strict regulations so bacteria don't evolve resistance as people may die from simple infections. It's also costly and slow to develop new ones
• Reducing Rate of Bacterial Development:

  • restricted agricultural antibiotic use
  • patients follow antibiotic course to kill all (none left to mutate/reproduce)
  • doctors not inappropriately prescribing antibiotics (non-serious infections)
• Darwin and Wallace developed the theory of evolution by observing Galapagos finches species and their differences despite originating from the same island:

  • beak shape
  • food source
  • hunting methods

  This suggested a common ancestor caused by desirable traits being passed down to adapt to different environments.
• All vertebrates have a pentadactyl limb (five-fingered limbs) which suggests evolution from a common ancestor.

  Over millions of years, the bones fused and changed due to natural selection for a creature to adapt such as humans with hands, whales with flippers and birds with wings.
• Classification - the organisation of living things into groups according to their similar physical traits, behaviours, diets and DNA
• There are currently 5 groups of classification but a 3 domain classification has been recently suggested as an alternative to other life classification systems because of the development of genetic analysis.
• Genetic analysis means we are able to determine and compare sequences of DNA bases and RNA sequences in similar ways
• 3 Domain Classification:

  • Archaea (primitive bacteria) - usually live in extreme environments with no nucleus and have unused sections of genes
  • Bacteria (true bacteria) - no nucleus or unused sections of genes
  • Eukaryota (including protists/fungi/plants/animals) - have a nucleus and unused sections of genes
• 5 Kingdom Classification:

  • Animal - multicellular with cells arranged as tissues/organs, nuclei, no cell walls
  • Plants - multicellular with cells arranged as tissues/organs, chloroplasts for photosynthesis, nuclei, cellulose cell walls
  • Fungi - multicellular apart from yeast, live on/in dead matter where they feed, nuclei, chitin cell walls
  • Protists - mostly unicellular, nuclei, cell walls made of different substances except chitin
  • Prokaryotes - unicellular, no nuclei, flexible cell walls
• New breeds and varieties are created so plants or animals can be more economically important or better quality for human consumption.

  This can be done by selective breeding or genetically modifying an organism.
• Genetic Modification - a process of changing the structure of a particular gene by moving one for two genes from one species to another
• Selective Breeding - when plants and animals with desired characteristics are artificially selected to breed so useful and attractive characteristics remain
• Selective Breeding:

  • crucial for high yields in agriculture (advantage)
  • used for medical research (advantage)
  • crops grow faster and cope with environmental conditions easier (advantage)
  • little variation means vulnerable to new diseases as there's less chance of resistance alleles (disadvantage)
  • causes inbreeding as gene pool is reduced causing mutations (disadvantage)
  • health problems causing genetic defects (disadvantage)
• Tissue culture - when an artificial medium of cells collected from living tissue is grown in a lab
• Tissue culture can be used for plant breeding programmes as it grows quickly in very little space all year round.

  The plants produced are clones (identical cells) which have the same beneficial features
• Plant tissue culture works by growing the small tissue pieces of the parent plant (root/shoot tips) in a growth medium containing nutrients and growth hormones.

  The environment must have aseptic (sterile) conditions to prevent harmful microbes growing
• Medical research uses animal tissue in isolation for experiments meaning the effects of a particular substance or environmental change can be seen without complications for the whole organism
• Animal Tissue Culture:

  1. Tissue sample extracted so cells can be separated using enzymes
  2. Place cells in a culture vessel
  3. Bathe cells in growth medium so they grow and multiply
  4. Split up cells in separate vessels after some cell division to encourage further growth and store for future use
• Genetic Engineering - the alteration of the genetic material of an organism by introducing foreign DNA into the genome

  This is usually done to introduce desirable characteristics including the use of enzymes and vectors.
• Genetic engineering with Enzymes:

  1. Restriction enzymes recognise specific DNA sequences and cut it at certain points which creates sticky ends
  2. Ligase enzymes join two DNA pieces together via sticky ends
  3. The recombinant DNA is formed
• Genetic engineering with Vectors:

  1. Recombinant DNA is formed with vector (plasmids and viruses)
  2. Plasmids are small circular molecules that transfer between bacteria while viruses insert DNA into infected cells
  3. Collect recombinant DNA and insert it into other cells that can use the inserted gene to produce more of the protein (e.g. bacteria with human insulin gene)
• Genetic engineering in Agriculture:

  • crops genetically modified to resist herbicides so farmers can spray crops to kill weeds which increases crop yield (advantage)
  • transplanted genes may enter the environment like herbicide-resistant weeds which could negatively affect food chains and human health (disadvantage)
• Genetic engineering in Medicine:

  • Bacteria produce human insulin (advantage)
  • Sheep/cows containing human genes produce useful proteins to be extracted like organ transplants and therapeutic antibodies for arthritis (advantage)
  • Concerned of the effect on the organism as many genetically modified embryos don't survive and animals suffer from health problems (disadvantage)
• Golden rice is a GM crop that has the genes from a daffodil and a bacterium in its genome to allow it to produce beta-carotene (Vitamin A) in its grains. Its mainly used in LICs and NEEs to help people with vitamin A deficiency
• Genetically engineering crops to be resistant to insect pests increases crop yields and reduces demand for chemical pesticides like Bt toxin which is poisonous to insect larvae
• The gene for Bt toxin is inserted into the stems/leaves of crops like corn and cotton which is specific to insects and not harmful to humans.

  However, long term exposure effects are unknown and insets constantly exposed may develop resistance (other insecticides are used to prevent this)
• GM crops can increase food production by being resistant to pests and growing better in drought conditions which will improve food security.

  However, may believe lack of food stems from poverty, countries becoming dependent on companies selling GM seeds and poor soil killing all types of crops
• GM crops could damage the environment and people:

  • toxic pollen could harm pollinating insects
  • can cause allergic reactions
  • people can absorb toxins (traces in blood)
  • unethical to interfere with nature
  • genes could harm other plants
  • more expensive
• Biological Control - when other organisms are used to control pests
• Biological control can decrease biodiversity as the pests could be eaten to extinction and other native insects could be eaten.

  However, it is safer for humans and the environment as toxic chemicals aren't needed
• Fertilisers contain minerals like nitrates/phosphates which are essential for crop growth.

  However, excess fertilisers can cause problems in rivers and lakes through eutrophication which can cause health problems in animals and people.