Genetic diversity and adaptation

• Genetic diversity

  The number of different alleles of genes in a population
• What does genetic diversity enable?

  Natural selection
• Benefit of genetic diversity

  More likely that individuals in a population will survive an environmental change.

  • Wider range of alleles= wider range of characteristics= greater probability that an individual will possess a characteristic that suits it to the new conditions
• Increasing genetic diversity within populations

  1. Genetic mutations (PRIMARY SOURCE) -> new alleles
  2. New alleles introduced- immigration from other populations
  3. Meiosis
  4. Random fertilisation of gametes during sexual reproduction
• Natural selection

  1. New alleles are formed by random mutations in genetic material.
  2. Many mutations are harmful, which may mean the individual with the mutated allele dies out, or the mutation is corrected by the proof-reading mechanism of the cell. Sometimes, the mutated allele is advantageous leading to an increased chance of survival and reproductive success.
  3. These individuals pass on their advantageous alleles to the next generation.
  4. Over many generations, the new allele increases in frequency in the population.
• Mutated alleles will only be passed on if...

  The mutations occur in the gametes.
• What is variation in traits caused by?

  Random mutations in genetic material
• What type of variation has a normal distribution?

  Continuous variation
• What are the different types of selection?

  1. Directional
  2. Stabilising
  3. Disruptive (A2)
• Directional selection

  • Individuals with alleles for extreme characteristics are more likely to survive and reproduce
  • e.g. antibiotic resistance
  • Mean shifts in the direction of the more favourable trait
  • The mean is equally common
  • Same distribution around the mean

  
• How does the frequency of a trait increase in a population?

  • Trait X has a genetic basis.
  • Random mutations over time -> genetic variation
  • Explain advantage (selection pressure) and type of selection
  • Individuals with this allele are more likely to survive, reproduce and pass on this allele to their offspring.
  • Over many generations, the frequency of this allele increases in the population and so therefore does the trait.
• Antibiotic resistance

  • Antibiotic resistance has a genetic basis
  • Random mutations over time lead to genetic variation in resistance to antibiotics- some individuals have alleles that give them a greater antibiotic resistance.
  • When the population is exposed to the antibiotic, bacteria with alleles that give them less resistance are killed.
  • Resistant bacteria survive, reproduce and pass on the allele for antibiotic resistance to their offspring.
  • Over many generations, the frequency of this allele increases in the population and so therefore does the trait.
• Stabilising selection

  • Individuals with alleles for characteristics towards the middle range are more likely to survive and reproduce.
  • Extremes of phenotypes are at a disadvantage.
  • Mean stays the same and is more common.
  • Smaller distribution about the mean.
  • e.g. human birthrate
• Human birth weights

  • Human birth weight has a genetic basis.
  • Random mutations over time leads to genetic variation in birth weight.
  • The selection pressure is surviving to a reproductive age. Very small babies are less likely to survive (large SA:V and weakened immune system) and very large babies can cause problems during childbirth.
  • Individuals with alleles more moderate birth weights are more likely to survive, reproduce and pass on their alleles for moderate birth weight to their offspring.
  • Over many generations, the frequency of this allele increases in the population and so therefore does the trait.

  
• Natural selection results in species that are better adapted to their environment.
• Behavioural adaptations


  The way an organism acts that increases its chance of survival.
• Physiological adaptations

  Processes inside an organism's body that increase its chance of survival.
• Anatomical adaptations

  The features of an organism's body that increase its chance of survival.