variation and evolution

• Variation


  Differences between individuals in a population
• Phenotype


  Observable characteristics of an individual
• What do genescode for?

  Code for proteins and the genome, which is all of your genes combined
• Apart from identical twins, everyone has a unique genome
• Environment


  Factors that influence how an individual looks and functions, in addition to their genes
• Most characteristics are determined by the interaction of genes and environment
• Mutation


  A change in the DNA code that may change the protein it codes for
• Most mutations don't have any effect on the proteins and so don't change the organism's phenotype
• Beneficial mutation


  A mutation that is advantageous, e.g. making an individual more resistant to disease or able to run faster
• Survival of the fittest

  The idea that the fittest individuals are more likely to survive and reproduce, passing on their beneficial traits
• Natural selection


  The process by which the fittest individuals are selected to survive
• Evolution


  The change in the inherited characteristics of a population over multiple generations, which can lead to the development of new species
• All current species must have evolved from different species sometime in the past
• All living species must have evolved from the simple life forms that first developed more than 3 billion years ago
• What does the term 'phenotype' mean?


  The observable characteristics of an organism
• Which two factors contribute to the variation between organisms? (exam answer) 


  An individual's characteristics are determined by both the genes they inherit, and the environment they're exposed to. This means that both contribute to the variation between organisms. Often the genes and environment will interact to create further variation.
• A change in the DNA code is called a mutation.
• What factor(s) are involved in determining body mass?

  Both genetic factors and environmental factors
• Factors determined entirely by genetic factors

  Natural eye colour

  Biological sex (male or female)
• Characteristics within a species can either show either 'continuous variation', or 'discontinuous variation'
• Continuous variation


  the characteristic changes gradually over a range of values, such as height, body mass, and skin colour. These characteristics are usefully influenced by multiple genes (polygenic).
• Discontinuous (discrete) variation 


  the characteristic has distinct forms, with no overlap. For example, eye colour is discontinuous because you have either blue, green, or brown eyes. These characteristics are usually only influenced by one or two genes. 
• Characteristics that show continuous variation

  Strength

  Hair colour
• Mutations generally have no effect, but are occasionally harmful, and very occasionally advantageous
• What does the phrase 'survival of the fittest' mean?


  The individuals with the most favourable characteristics are most likely to survive
• Evolution is the process by which the inherited characteristics of a population change over time due to natural selection. In some cases, this may result in the formation of a new species.
• Who is credited with developing and proposing the theory of evolution?

  Charles Darwin
• What provides evidence for the theory of evolution?

  The spread of antibiotic resistance

  Fossil records
• Describe a series of events that might result in zebras evolving to run more quickly.


  1. There is variation among the zebra population so that some can run faster than others
  2. A mutation arises that allows some zebras to run faster
  3. Those zebras that can run fastest are more likely to survive...
  4. ... and are therefore more likely to reproduce and pass on their advantageous alleles
  5. This repeats over multiple generations
  6. So the advantageous allele spreads throughout the population, until the species has 'evolved' to run faster
• Speciation is the evolutionary process by which populations evolve to become distinct species.
• Environmental variation


  characteristics can also be caused by an organism’s environment, but these changes are generally not heritable (there is no change in the DNA of the organism). For example, a child who does not receive adequate nutrition will not grow to their full height, however, this does not affect their potential height as determined by their genetics.
• Genetic variation 


  different characteristics can arise as a result of both random mutation and sexual reproduction. Random mutation occurs in gametes to

  produce offspring with ‘brand new’ phenotypic characteristics, whereas sexual reproduction causes the offspring to have a new combination of characteristics from both its mother and its father.
• Most phenotypic features are the result of multiple genes acting together, and not single genes.
• Some mutations can have a small effect on the phenotype, and other mutations, rarely, can significantly affect the phenotype - for example, changing one base can change one amino acid in a protein. If the protein was an enzyme, this has the potential to change the shape of the active site so that substrates can no longer bind to it.