Population Genetics 4/4

• Genetic variation


  The variety of genes within a population, including different alleles and the frequency at which they occur
• Higher genetic variation

  • Gives a more adaptable population that is better suited to respond to environmental changes (fitter)
  • Populations with a wide range of genetic variation are more likely to have individuals that can adapt to survive in new conditions
• Low genetic variation


  • Makes a population more vulnerable as there are less individuals that can adapt to survive in new conditions
  • If an environment changes, the entire species would be at risk
• Natural selection


  • A driver of evolution that occurs when populations of organisms face selection pressures
  • The process by which beneficial traits in a population tend to be preserved while unfavourable traits are likely to be eliminated
• Selection pressures


  • Evolutionary forces that cause a particular phenotype to be more favourable in certain environmental conditions
  • Examples: predation, competition, diseases, food scarcity, droughts etc.
• Fitness


  • The ability of a particular genotype to survive to reproductive age, find a mate and produce offspring
  • The more offspring an organism produces during its lifetime, the greater its fitness
  • An organism's fitness reflects how well it is adapted to its environment and its ability to survive selection pressures
• Natural selection


  1. Fitter organisms survive and pass their genes onto their offspring

  2. Producing a population that is better adapted to the selection pressures of the environment

  3. Genes of less fit individuals are less likely to be passed onto the next generation

  4. More favourable alleles survive (higher frequency)

  5. Less favourable alleles do not survive and fade out (less frequency)
• Types of selection

  • Stabilising
  • Directional
  • Disruptive
• Adaptations


  • Features that organisms have evolved to be successful in their environment (higher fitness)
  • Adaptations allow the organism to survive, reach reproductive maturity, find mates and produce offspring successfully
  • Adaptations arise over many generations through the process of natural selection
• Types of adaptations

  • Structural (body functions and how it looks like on the outside, e.g. fur)
  • Behavioural (how an organism acts, e.g. hibernating)
  • Physiological (how the organism's body functions on the inside, e.g. changes in cells)
• Population bottleneck


  • When a population undergoes a significant reduction in numbers due to a catastrophic event, leaving very few survivors
  • Leads to reduced genetic variation
• Inbreeding depression


  • Reduced fitness as a result of inbreeding
  • Occurs when closely related individuals mate, as both parents are likely to carry the same undesirable alleles causing offspring to inherit harmful alleles
  • Leads to undesirable traits and genetic disorders
  • Makes a population more vulnerable, often resulting in lower fertility rates, higher susceptibility to diseases, reduced growth rates and increased mortality
• Migration


  • When organisms move from one population to another
  • Leads to the transfer of alleles from one population to another (gene flow)
• Gene flow


  • The movement of genes in or out of a population
  • Occurs when organisms migrate to another population and successfully interbreed, introducing new alleles that may have been absent or less frequent in the receiving population
• Benefits of gene flow

  • Improved ability to survive - Increased genetic variation provides a buffer against environmental changes
  • Dilute harmful genetic traits - Mixing genes from different pools makes detrimental alleles less common, leading to a healthier population
• Founder effect


  • When a small number of individuals from a larger population establish a new isolated population
  • The new population may not have all the alleles from the old population, so it is not as genetically diverse
  • The main cause of the founder effect is migration