18 - Populations & Evolution

• What is the Gene Pool?

  All the alleles of all the genes in a population at a particular time
• What is the Allele Frequency?

  The proportion of each allele for a gene in a gene pool
• What are the two formulae for the Hardy-Weinberg principle?

  1. p2 + 2pq + q2 = 1
  2. p + q = 1
• What do the following represent in the Hardy-Weinberg formula?

  p = frequency of the dominant allele

  q = frequency of the recessive allele

  p^2 = frequency of homozygous dominant genotype

  2pq = frequency of heterozygous genotype

  q^2 = frequency of homozygous recessive genotype
• Cystic fibrosis is caused by a recessive allele 0.02% of the UK population suffer from cystic fibrosis. What proportion of the UK are carriers?

  3% (2.76%)

  
• Within a population of a species, there can be a wide range of phenotypes. What are the two overall causes of this?

  1. Genetic Factors
  2. Environmental Factors
• What are 3 selection pressures that can drive natural selection?

  1. Predation
  2. Disease
  3. Competition
• What is evolution?

  The change in the allele frequency over many generations in a given population
• What are the three types of selection that occur?

  1. Stabilising
  2. Directional
  3. Disruptive
• Which type of selection leads to speciation?

  Disruptive
• What type of selection is this?

  Stabilising

  
• What type of selection is this?

  Directional

  
• What type of selection is this?

  Disruptive

  
• What is meant by Genetic Drift?

  The change in the allele frequency within a population between generations.
• Does genetic drift have a bigger impact on smaller or larger populations?

  The smaller a population, the greater the proportional impact changes in allele frequencies will have. This is why evolution often occurs more rapidly in smaller populations.
• What is meant by Speciation?

  Speciation is the process that results in the creation of new species.

  
• What is meant by Allopatric Speciation?

  When a population becomes reproductively isolated due to geographical barriers
• What is meant by Sympatric Speciation?

  When changes in reproductive mechanisms cause speciation, without geographic isolation
• Different species of palm tree, all located on the same island, flower at different times of the year. All these palm trees have a common ancestor. Describe how new species of palm trees would have arisen (5 marks)

  1. Occurs in the same habitat (sympatric speciation)
  2. Mutation causes different flowering times
  3. Reproductive isolation/no gene flow
  4. Different alleles passed on
  5. Disruptive (natural) selection;
  6. Eventually different species cannot (inter)breed to produce fertile offspring