Genetic Diversity & Adaptation

• Genetic Diversity

  • INCREASED: with MUTATIONS (in the DNA forming new alleles) or DIFFERENT ALLELES (being introduced in a population caused by migration of individuals from another population reproducing with another- known as Gene Flow)
• GENETIC BOTTLENECKS/ THE BOTTLENECK EFFECT:

  • GENETIC BOTTLENECKS: Reduces genetic diversity

  1. Original population= high variation
  2. Something happens (eg environment changes) -> reduces population significantly
  3. One group of the population may have an allele which benefits their survival -> only they will live 
  4. No longer high genetic diversity in population, survivors reproduce which creates new population that has the group with the benefiting allele as dominant over the other groups
• FOUNDER EFFECT:

  • Type of genetic bottleneck, when a few organisms from a population start a new colony.
  • Due to the small number of individuals= small number of different alleles in the gene pool
  • Often leads to more genetic disorders (due to the lack of new alleles being introduced in the population)
  • Eg the Amish people in North America have remained isolated from the surrounding population, and the lack of genetic diversity had led to a high incidence of certain genetic disorders
• Natural Selection

  • NATURAL SELECTION: When advantageous alleles within a population increases due to it benefiting the organisms survival chances (random)
  • Decreases biodiversity- only organisms with advantageous alleles survive
  • MUTATIONS: Randomly occurring mutations -> (sometimes) new allele formed: harmful (-> mutated gene quickly dies out) or beneficial (-> increases chance of an organism's survival)
• EVOLUTION:

  1. Organisms with beneficial genes/ characteristics= more likely to survive long enough to mate
  2. This means the beneficial genes are passed on to the next gen
  3. The next gen will have a greater probability of inheriting their genes 
  4. The offspring are more likely to survive, reproduce, & pass on their genes
  5. So the frequency of beneficial alleles increases from gen to next gen
  6. Over generations, this leads to evolution as advantageous alleles become more common in the population
• EVOLUTION:

  • EG GIRAFFES: There were giraffes with short and long necks, however short necked giraffes could not reach as much food as the long necked giraffes so only the long necked giraffes survived. The beneficial allele for long necks allowed those individuals too reach food, survive long enough to mate, and pass this allele to the next generation
• SELECTIVE BREEDING:

  • Also decreases biodiversity- only organisms (eg crops or livestock) are allowed to breed, so the other alleles disappear from the population
• SURVIVAL AND REPRODUCTION ADAPTATIONS:

  • BEHAVIOURAL: Acts/ behaviour the organism does to increase chances of survival/ reproduction (eg courting behaviour)
  • PHYSIOLOGICAL: Processes inside the body that increases an organism's chance of survival/ reproduction (eg antifreeze within fish that allow them to survive freezing temperatures)
  • ANATOMICAL: Structural features that increases chances of survival/ reproduction (eg some animals have sharp claws for digging burrows)
• EG OF ADAPTATIONS OF AN ANIMAL- POLAR BEAR:

  • BEHAVIORAL: Pregnant polar bears make dens to prepare for the winter
  • PHYSIOLOGICAL: Body temperature is maintained through insulated fat & a thick layer of fur
  • ANATOMICAL: Large paws to distribute weight over a large surface area in the snow
• EG OF ADAPTATIONS OF A PLANT- CACTUS:

  • BEHAVIORAL: Reduced demand for water as they grow slowly
  • PHYSIOLOGICAL:  Stomata opening and closing at different times eg minimal photosynthesis in the midday
  • ANATOMICAL: Reduced surface area (no leaves)
• • GENOTYPE: Alleles for genes (eg Bb/ BB/ bb)

  PHENOTYPE: Expressed characteristics (eg blue eyes)
• DISRUPTIVE SELECTION: (disrupt= opposite to stable (not normal))

  • Environmental change that makes the median at a disadvantage
  • Ties into speciation
  • Eg beak sizes in birds ( if seeds are only either very small or very large, natural selection will favour birds with with very small or very large beaks- not the median)
• STABILISING SELECTION: (stable= becoming normal (the median))

  • More dominant trait -> fewer variation
  • More individuals become the average, more pressure against extremists
  • Most common selection
  • Environment is not changing, reducing possibility of a range of characteristics
  • Eg robins laying typically 4 eggs (larger clutches -> (may) malnourished chicks & smaller clutches -> (may) no viable offspring)
• DIRECTIONAL SELECTION: (changing direction )More dominant trait -> fewer variation

  • Environmental change -> one extreme becomes dominant over the other, becomes advantageous
  • Eg speckled/ white moths to black moths due to change in the environment (light to dark trees) so black moths now camouflage more efficiently
• NORMAL DISTRIBUTION GRAPHS: (include directional)