SB4 Natural Selection and Genetic Modification


SB4a Evidence for Human Evolution

  • Evolution - gradual change in the characteristics of a species over time. 
  • Fossils - scientists can work out how old the fossils are and put them in order, however, they don't show gradual change.
  • Ardipithecus ramidus (Ardi)- 4.4 million, Australopithecus afarensis (Lucy)- 3.9 - 3 million, Homo habilis - 2.4 - 1.4 million, Homo erectus - 1.8 - 0.5 million, Homo sapiens - 195 000.
  • Stone tools - scientists can work out ages of the rock. The oldest stones were simple and more recent rockers were more sophisticated. 
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SB4b Dawin's Theory

  • Genetic variation - the characteristics of individuals vary (due to differences in genes).
  • Environmental change - conditions in an area change. E.g. the lack of resorces causes more competition between organisms. 
  • Natural selection - by chance, the variations of some individual make them better at coping with change than others, more likely to survie ('survival of the fittest').
  • Inheritance - the survivors breed and pass on their variations to their offspring. So the next generation contains 'better-adapted variations'.
  • Evolution - if the environmental conditions remain unchanged, natural selection occurs until all individulals have the 'better-adapted variations'.
  • Antibiotics and bacteria - Some bacteria in a population are more resistant than others. with time, the antibiotics kill more bacteria. The most resistant take the longest to die. The resistant bacteria survive and reproduce, leaving a whole population that are now resistant.  
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SB4c Development of Darwin's Theory

  • The theory was slow to be accepted because it challenged god. 
  • Darwin couldn't explain how variation occurred, and the evolution of characteristics of fossils was not gradual.
  • Pentadactyl limb - vertebrates have limbs with five fingers. The limb suggests evolution from a common ancestor and not that the bones were designed for specific purposes independently of one another.
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SB4d Classification

  • Carl Linnaeus - divided organisms on what they look like, by kingdoms. Characteristics of the organisms in a group got similar as groups got more smaller. Linneaus used the last two groups (genus and species) to give each organism its binomial name. 
  • There are 5 kingdoms: Animals (multicellular, has nuclei and no cell walls), Plants (multicelllular, chloroplasts, cellulose cell wall), Fungi (multicellular, chitin cell walls), Protists (unicellular, some have cell walls, not chitin) and Prokaryotes (unicellular, no nuclei and flexible cell walls).
  • Carl Woese - divide into three domains: Archaea (cells no nucleus, unused sections of DNA), Bacteria (cells no nucleus, no unused sections in genes) and Eukarya (cells with nucleus, unused sections in genes). 
  • The more DNA two organisms have in common, the more recently they evolved from a common ancestor and closely related they are. 
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SB4e Breeds and Varieties

  • Artificial selection - humans chose certain organisms because they have useful characteristics , such as sheep with thick wool. 
  • Selective breeding - when human chose certain organisms because of certain characteristics, and breed them until the chosen characteristics more and more obvious. Produces new breeds of animal species and new varieties of plant species. 
  • Plants and animals are often bred for: disease resistance, yield, coping with environmental conditions, fast growth and flavour. 
  • Genetic engineering - changing DNA of one organism (its genome), often by inserting genes from another. This creates genetically modified organisms (GMO). Much faster than artificial selection but more expensize. 
  • GMOs are resistance to disease-causing organisms, and others grow larger and faster than normal. 
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SB4f Tissue Culture

  • Tissue culture - growing of cells or tissues in a liquid containing nutrients or on a solid medium. This forms a callus (clump of undifferentiated cells), and are treated to become specialised.
  • Tissue culture is used to produce new plants on the risk of extiction. It is also used to produce new individuals of plant that may be difficult to grow from seed. 
  • Cell cultures are used to study virsuses, which cannot replicate outside of cells. 
  • Using cell cultures is a way of testing new medicines withoug harming animals or humans.
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SB4g Genes in Agriculture and Medicine

  • Selective breeding risks - only certain alleles are selected. Others become rare or disappear, So, alleles that might be useful in the future are no longer avaliable. 
  • Farming huge numbers of the same breed and variety is a problem as if the change in conditions affect one organism, all the others are affected. 
  • GM crops have been produced to be resistant to some insects, so less herbicide is needed, however, seeds are expensive and some people think that they will pass on their genes to wild plants. 

Genetic enginerring of bacteria: 

  • Restriction enzymes make staggered cuts in DNA molecules, producing sections with a few unpaired bases at each end - 'sticky ends'. A section of DNA containing the gene for insulin is cut from chromosome. 
  • SAME Restiction enzyme is used to cut plasmid open, so it has same 'sticky ends'. 
  • Sections of the DNA is mixed with cut plasmid (recombinant DNA), sticky ends pair up and ligase enzyme is used to join ends together. 
  • Plasmids are inserted back into bacteria which are grown in huge tanks and insulin is easily extracted. 
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SB4h GM and Agriculture

  • When insects eat a crop, it reduces it yield - called pests. They can be controlled by spraying crop with chemical insecticides .
  • Advatages with GM is that is affects the insect when it chews the plant. Insecticide could kill a wide range of insect species, and insect predators remain unharmed by GM crops as they don't eat the crop. 
  • Disadvantage - insects can become resistant to GM crops. GM crops are more expensive. 
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SB4i Fertilisers and Biological Control

  • Biological control - using organisms to control pests 
  • Biological control, GM organisms and selective breeding can all help to increase yield of food. 
  • Fertilisers are used to increase growth and yield of crops. 
  • Mineral salts are naturally occuring compounds, which plants need to produce new substances. Fertilisers contain these, which plants absorb to make healthy new cells. 
  • Some may not be absorbed and could get into nearby streams or lakes. This causes pollution and lead to death of organisms. 
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