10. inheritance

• Genetic drift is the change in the composition of a gene pool as a result of chance or random events

  • It will occur faster and be more significant in smaller populations, where chance events have a bigger impact on the gene pool
  • Larger populations will be less affected by random events and maintain more stable allele frequencies with low genetic drift
• Allele frequencies will change significantly when a large population is reduced to a small population. Two mechanisms by which this population change may occur:

  1. Population bottleneck
  2. Founder effect
• Founder Effect

  The founder effect occurs when a small group breaks away from a larger population to colonise a new territory

  • As this population subset does not have the same degree of diversity as a larger population, it is subject to more genetic drift
  • Consequently, as this new colony increases in size, its gene pool will no longer be representative of the original gene pool
  • The founder effect differs from population bottlenecks in that the original population remains largely intact
• Population Bottlenecks

  Population bottlenecks occur when an event reduces population size by an order of magnitude (~ >50%)

  • These bottlenecks may result from natural occurrences (e.g. fires, floods, etc.) or be human induced (e.g. overhunting)
  • The surviving population has less genetic variability than before and will be subject to a higher level of genetic drift
  • As the surviving members begin to repopulate, the newly developing gene pool will be divergent to the original
• Isolation can lead to the development of a new species because...

  • The two populations were separated by a physical/geographical barrier OR were reproductively isolated
  • Exchange of genes not possible between the two populations
  • Different alleles are selected for each population (due to different environmental conditions)
  • Natural selection leads to the development of a new species
  • Speciation has occurred between the two populations
• Wolves have been domesticated over many years in the following way:

  • Selective breeding has been carried out
  • Puppies with desirable tendencies are selected
  • These are bred together
  • The process is repeated over many generations of wolves
  • Eventually, a more domesticated / human dependent / less aggressive dog will be produced
• The chi-squared test is used:

  • To determine associations between species / groups of data (collected from the mesocosm)
  • By comparing observed results with expected results
  • To establish significance (of an association) OR to show whether results are due to chance or not
  • If the chi-squared value is higher than the critical value, the null hypothesis can be rejected / the association is significant