Diversity and selection

• What is a population?


  The number of individuals of the same species that live in the same place and can interbreed.
• A wider range of alleles means a wider range of characteristics so a greater probability that an individual in the population will have a characteristic that will suit the environment.
• What is an adaptation?


  Features that increase an organisms chance of survival and reproduction.
• How to adaptations develop?

  Natural selection
• What are the 3 types of Adaptations?


  Behavioural, Physiological and Anatomical/structural
• What is a Behavioural adaptation?


  Ways an organism acts to increase chance of survival.

  e.g possums play dead
• What is a Physiological Adaptation?


  Processes inside an organisms body that increases its chance of survival.

  e.g Some bacteria produce antibiotics
• What is an Anatomical/Structural Adaptation?


  Structural features of an organisms body that increases its chance of survival.

  e.g Whales have thick blubber
• How does Antibiotic resistance happen?

  There is a population of Bacteria with variation

  One variant is resistant to the antibiotics

  Antibiotics kill the non-resistance variants

  The resistant variant survives and reproduces and passes on the resistant allele

  The frequency of the resistant allele increases in the population.
• What is Selection?


  The process where organisms that are better adapted to their environment tend to survive and breed.

  Different environmental conditions favour different charecteristics.
• What are the 2 types of Selection?


  Directional and Stabilising.
• What is Variation?


  Differences that exist between individuals.

  (This is what selection starts with)
• What is continuous variation? 


  Individuals in a population vary within a range.
• Most characteristics are influenced by more than just one gene.


  polygenes= these characteristics are influenced by the environment
• How do we Investigate variation?

  We use the mean and standard deviation to measure how much variation there is in a sample.

  Most samples will include values either side of the mean (you end up with a normal distribution curve symmetrical about the mean)
• What is directional selection?


  This happens when there is a change in environment,

  If an organism has a selective advantage more of the species will have its characteristics so an alternative phenotype will become more common and the mean and standard deviation graph shifts.
• What is stabilising selection?


  This happens when the environment is stable,

  selection acts against both extremes in a range of phenotypes lowering variation but keeping the mean in the same position.

  (it could reduce their ability to adapt)
• Natural selection:

  1. within any population of a species there will be a gene pool containing a wide variety of alleles.
  2. Random mutation of alleles may result in a new allele of a gene (will be harmful in most cases).
  3. In certain environments, the new allele might give an organism an advantage over other individuals.
• Natural selection part 2:

  1. These individuals are better adapted and more likely to survive in the competition for survival.
  2. These adapted individuals are more likely to obtain resources, live longer and reproduce.
  3. Those that reproduce successfully will pass on alleles to the next generation
  4. New individuals also have advantageous allele- so are more likely to survive and reproduce as well.
  5. Over many generations, number of individuals with advantageous allele will increase while those with less advantageous alleles will decrease in number.