variation and evolution

• what is variation 


  differences in the characteristics of individuals in a population is called variation.
• What are the two causes of variation within a species?

  • Genetics
  • Environment
  • A mixture of both of 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 creates genetic variation in a species?

  • Spontaneous mutations
  • Sexual reproduction
• what is a mutation


  a random change to the base sequence in DNA which results in genetic variants.

  They occur continuously.
• state the three types of gene mutation

  • Insertion
  • Deletion
  • Substitution
• How may a gene mutation affect an organism's phenotype?

  • 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 a 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?

  • Agradual 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 have evolved from simple life forms that first developed more than 3 billion years ago.

  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.
• 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 humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes.
• Outline the main steps involved in selective breeding

  1. Identify a desired characteristic e.g. disease resistance.
  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.
• give examples of characteristics selected for in 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 desirable features:

  • Crops produce a higher vield of grain
  • Cows produce a greater supply of milk
  • Plants produce larger fruit
  • Domesticated animals
• other than in agriculture where else is selective breeding useful

  • In medical research
  • In sports e.g. horse racing
• outline the 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.
• what is genetic engineering

  • The modification of the genome of an 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 cells of other organisms.
  • Enables the formation of an organism with beneficial characteristics.
• give examples of uses for genetically modified plants

  • Disease resistance
  • Produce larger fruits
• what is a use for genetically modified bacteria cells

  to produce human insulin to treat diabetes mellitus.
• describe the benefits of genetic engineering

  • Increased crop yields for growing population e.g. herbicide-resistance, disease-resistance.
  • Useful in medicine e.g. insulin-producing bacteria, anti-thrombin in goat milk, possibility to overcome some inherited disorders (being explored in medical research).
  • GM crops produce scarce resources e.g. GM golden rice produces beta-carotene (source of vitamin A in the body).
• describe the risks of genetic engineering

  • Long-term effects of consumption of GM crops unknown.
  • Negative environmental impacts e.g. reduction in biodiversity, impact on food chain, contamination of non-GM crops forming 'superweeds'.
  • Late-onset health problems in GM animals.
  • GM seeds are expensive. LEDCs may be unable to afford them or may become dependent on businesses that sell them.
• What is the name for crops that have had their genes modified?

  genetically modified (GM) crops e.g. those modified to be resistant to insect attack and herbicides.
• What is Bacillus thuringiensis (Bt)?

  • Insect larvae are harmful to crops.
  • Bt is a bacterium which secretes a toxin that kills insect larvae.
• How is genetic engineering used to protect crops against insects?

  • The gene for toxin production in Bt can be isolated and inserted into the DNA of crops.
  • Bt crops now secrete the toxin which kills any insect larvae that feed on it.
• What are the benefits of Bt crops?

  • Increased crop yields (fewer crops damaged).
  • Lessens the need for artificial insecticides.
  • 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 process of genetic engineering

  1. DNA is cut at specific base sequences by restriction enzymes to create sticky ends.
  2. Vector DNA cut using the same restriction enzymes to create complementary sticky ends.
  3. Ligase enzymes join the sticky ends of the DNA and vector DNA forming recombinant DNA.
  4. Recombinant DNA mixed with and 'taken up' by target cells.
• what is a vector

  a structure that delivers the desired gene into the recipient cell e.g. plasmids, viruses.