Genetic Diversity And Adaptation

• Define genetic diversity


  Number of different alles of genes in a population
• What increases genetic diversity within a population

  Mutations in the DNA

  Different alleles being introduced into a population from another population ( migration)
• Explain what reduces genetic diversity

  Genetic bottleneck - reduces number of different alleles
• What is the founder effect? Give an example.

  When just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool

  e.g. Amish people ( Swiss --> NA)
• Define populations

  = Group of organisms of the same species in a particular habitat at one time.
• What factors cause genetic diversity?

  - Gene mutation

  - Chromosome mutation

  - Random factors associated with meiosis and fertilisation
• Define selection

  = Process by which organisms better adapted to their environment are more likely to survive and reproduce.
• Define directional selection

  = Selection favouring individuals that vary in one direction from the mean of the population.

  
  

  => changes overall characteristics in the population.
• Outline an example of directional selection

  - Antibiotic resistance with penicillin:

  
  

  1. Spontaneous mutation in allele of a gene in a bacterium ---> new protein (enzyme - penicillinase) produced.

  
  

  2. Bacterium in situation where penicillin being used to treat an individual (by chance) ---> mutation gives bacterium an advantage as it can produce penicillinase and survive.

  
  

  3. Surviving bacterium divides by binary fission ---> small population of resistant bacteria forms.

  
  

  4. Population of resistant bacteria grows at expense of non-resistant population

  => allele frequency of penicillinase allele increases in the population.

  
  

  => normal distribution curve shifts in direction of higher penicillin resistance.

  
  

  => antibiotic use places a directional selection pressure on the bacterial population.
• Define stabilising selection

  = Selection favouring individuals with the average characteristic of the population.

  
  

  => preserves overall characteristics of the population.
• Outline an example of stabilising selection

  - Human birth weights:

  
  

  1. Infant mortality rate lowest in range 2.5-4.0 kg and increases either side of this range.

  
  

  2. Mortality rate is greater at the two extremes => population's characteristics are being preserved rather than changed ---> phenotypes around the mean of the population selected for and those at both extremes selected against.
• What is the result of natural selection?

  Results in species better adapted to the environment in which they live.
• What are the types of adaptations of natural selection?

  Anatomical - Structural features e.g layer of blubber

  Physiological - Processes inside body e.g. hibernation lowers rate of metabolism

  Behavioural - Way an organism acts e.g. possums playing dead