Variation and Evolution

• What is variation?

  Differences in the characteristics of individuals in a population is called variation.
• What are the causes of variation in species

  -Genetics

  -Environment

  -A mixture of both the above
• What is genetic variation?

  Variations in the genotypes of organisms of the same species due to the presence of different alleles

  Creates differences in phenotypes.  
• What causes genetic variation in species? 

  Spontaneous mutations

  Sexual reproduction   
• What is mutation?

  A random change to the base sequence of DNA which results in genetic variants. They occur continuously. 
• State the three types of gene mutation:

  Insertion

  Deletion

  Substitution 
• How may a gene affect an organism's phenotype? (3)

  -Neutral mutation does not change the sequence of amino acids. Protein structure and function same. No effect on phenotype.

  -Mutation may cause a minor change in an organism's phenotype e.g change in eye colour

  -Mutation may completely change the sequence of amino acids. This may result in non-functional protein. Severe changes to phenotype.  
• What is the consequence of a new phenotype caused by a mutation being suited to an environmental change? 

  There will be a rapid change in the species.  
• What is evolution?

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

  Occurs due to natural selection which may result in the formation of a new species.   
• Outline the theory of natural selection  

  All species of living things evolved from simple life forms that developed more then 3 billion years ago.

  1.   Genetic variation exists due to spontaneous mutations
  2. Selection pressure (e.g competiton, 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 benefical alleles
  6. Frequency of advantageous alleles increase   
• How do two populations become different species?   

  When their phenotypes become different to the extent that they can no longer interbreed to produce fertile offspring.
• What is selective breeding.   

  The process by which human artifically select organisms with desirable characteristics and breed them to produce organisms with similar phenotypes.   
• Outline the main steps involved in selective breeding. 

  Identify a desired characteristic e.g disease resistance

  Select parent organisms that show desired traits and breed them together

  Select offspring with the desired traits and breed them together.

  Process is repeated until all offspring have the desired traits.       
• Give examples of characteristics selected for selective breeding.  

  Disease resistance in crops

  Higher milk or meat production in animals

  Gentle nature in domestic dogs

  Large flowers
• What is the main advantage of selective breeding? 

  Creates organisms with desired features:

  • Crops produce a higher yield of grain
  • Cows produce greater milk supply
  • Plants produce larger fruit
  • Domesticated animals 
• Other than agriculture, where is selective breeding useful? 

  In medical research

  In sports e.g. horse racing 
• Outline the disadvantages of selective breeding (4)  

  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  
• What is genetic engineering?

  The modification of the genome of the organism by the insertion of a desired gene from another organism - genes from chromosomes of humans and other organisms can be 'cut out' and transferred to the cells of other organisms

  Enables the formation of an organism with benefical characteristics
• Give examples of uses for genetically modified plants.

  Disease resistance

  Produce larger fruit
• What is a use for genetically modified bacterial cells?

  To produce human insulin to treat diabetes
• Describe the benefits of genetic engineering (3)

  Increased crop yields for growing population e.g. herbicide-resistance, disease-resistance

  Useful in medicine e.g. insulin producing bacteria

  GM crops produce scarce resources e.g GM golden rice that provides vitamin A   
• Describe the risks of genetic engineering. (4)

  Long-term effects of consumption of GM crops unknown

  Negative environmental impacts such as reduction in biodiversity

  Late-onset health problems in GM animals

  GM seeds are expensive. LEDCs may be unable to afford them.  
• What is the name for crops which had their genes modified?

  GM (Genetically modified)
• What is Bacillus Thuringiensis (Bt)?

  Insect larvae are harmful to crops

  Bt is a bacterium that produces toxins that kills insect larvae
• How is genetic engineering used to protect crops against insects?

  -the gene for the toxin production in Bt can be isolated and inserted in the DNA of crops.

  -Bt crops now secrete the toxin which kills many insect larvae that feed on it. 
• What are the benefits of Bt crops? (3)

  -Increased crop yields (fewer crops damaged)

  -Lessens the need for artifical pesticides

  -Bt toxin is specific to certain insect larvae so is not harmful to other organisms that ingest it.  
• What are the risks of Bt crops?

  -Long term effects of consumption of Bt crops unknown

  -Insect larvae may become resistant to the Bt toxin

  -Killing insect larvae reduces biodiversity.
• Describe the processes of genetic engineering? (Higher)

  DNA is cut at specific base sequences by restriction enzymes to create sticky ends.

  Vector DNA cut using the same restriction enzymes to create complementary sticky ends.

  Ligase enzymes join the sticky ends of the DNA and vector DNA forming recombinant DNA.

  Revombinant DNA mixed with and 'taken up' by target cells.        
• What is vector?

  A structure that delivers the desired gene to the recipient cells