Genetic diversity and adaptation

• What is genetic diversity?

  The variety and number of different alleles in a population of a species.
• Genotype vs phenotype

  A genotype is the alleles an individual possesses, and the phenotype is how the genotype is expressed.
• Why is genetic diversity important?

  A greater range of phenotypes means that a population is more likely to adapt to environmental change as certain phenotypes are more adapted to that change, and will survive and pass the advantageous allele down.
• 3 factors that can reduce genetic diversity:

  Genetic bottleneck, founder effect and artificial selection.
• What is genetic bottleneck?

  Reduction in genetic diversity due to a sharp decrease in population size after a catastrophic event.
• What is the founder effect?

  The loss of genetic variation that occurs when a small group of individuals within a species establishes a new population.
• What is artificial selection?

  Artificial selection is the process of intentionally breeding plants or animals with specific traits in order to produce offspring with those desired traits based on their alleles.
• Step-by-step of effects of genetic bottleneck:

  1. Population size reduced
  2. Genetic diversity reduced
  3. Population less likely to adapt to environmental changes
  4. Inbreeding occurs
  5. This restricts the already lowered genetic diversity
• Disadvantages of selective breeding

  -> Genetic diversity is reduced

  -> In plants, they are outcompeted by wild plants and susceptible to drought

  -> In animals, certain alleles that cause genetic disorders are perpetuated

  -> ethical implications as there is an increase of abnormalities and animal welfare is at risk
• What is genetic drift?

  Genetic drift is the random fluctuation of allele frequencies in a population over time, leading to changes in the genetic makeup of the population. More prominent in founder populations.
• An increased founder effect can decrease...

  ...heterozygosity because genetic diversity is lower.
• Define polygenic:

  A single characteristic that is controlled by many genes e.g. height or weight.
• Define non-polygenic:

  A single characteristic that is controlled by one or two genes e.g. blood group.
• Interspecific vs intraspecific variation:

  Interspecific= between different species

  Intraspecific= within a species
• Causes of genetic variation:

  1. Mutations- sudden change in DNA forms new chromosomes which may be passed on to subsequent generations. (only cause of genetic variation in asexually reproducing organisms)
  2. Meiosis- nuclear division which forms gametes, where genetic information is mixed up so they are all different.
  3. Fertilisation- fusion of gametes so adds further variation to offspring.
• Causes of environmental variation:

  Changes the phenotype.

  e.g. temperature, rainfall, sunlight, soil conditions, food availability
• Continuous vs discontinuous variation:

  Continuous- non categoric range of phenotypes for a trait caused by multiple alleles or lots of genes interacting. Can be affected by the environment.

  Discontinuous- categoric phenotypes for a trait caused by 1 or 2 alleles and the trait is non-polygenic. Mainly unaffected by the environment.
• What are monozygotic twins?

  Twins who are genetically identical so they share 100% of their DNA.
• What are dizygotic twins?

  Twins who share 50% of their DNA as they are a product of two eggs fertilised by two different sperm at the same time. They are fraternal.
• Monozygotic twin study:

  The twins are reared into different environments and are then tested for their phenotypes and how similar they are.

  If there is a high concordance in the results, then the characteristic is mainly genetically controlled, whereas a low concordance indicates environmental control.
• Dizygotic twin study:

  The twins are reared together then tested for their phenotypes.

  A high concordance means that the characteristic is mainly environmentally controlled, whereas a low concordance means it is mainly genetically controlled.
• Disadvantages of the twin case studies:

  1. Ethical issues with rearing monozygotic twins separately.
  2. Sampling of the twins can be biased.
  3. Sample size of monozygotic twins is very small.
• What are selection pressures?

  They can be abiotic (e.g. temperature, water) or biotic (e.g. predators, disease).

  They affect the chance of survival of an organism.
• What is directional selection?

  Selection against one extreme.

  A selection pressure causes phenotypes away from the mean phenotype to be selected, so the mean shifts towards one extreme.
• What is stabilising selection?

  Selection against both extremes.

  Occurs in a stable environment where there is little change in the abiotic factors of the environment.

  The mode/mean is selected more commonly so the population of extremes decreases.
• What is disruptive selection?

  Selection that favours extreme phenotypes over moderate ones.

  It leads to speciation.
• 2 types of isolation:

  1. Allopatric- geographical isolation creates two separate populations
  2. Sympatric- behavioural or physiological isolation which creates a new population within the original one.
• Reasons for isolation:

  Geographical, behavioural and structural/physiological.

  These all result in reproductive isolation.
• What does a high rate of gene flow between populations result in?

  Increased genetic differences.
• What role does genetic drift play in speciation?

  It can lead to divergence in isolated populations.
• What does a high survival rate of individuals with a specific trait indicate?

  Increased allele frequency.
• What is species diversity?

  A measure of the number of different species and the number of individuals of each in a habitat.
• What is species richness?

  The number of different species present in a given area or ecosystem.
• What is species evenness?

  The relative abundance of different species within a community.
• How to calculate species diversity:

  d= N(N-1) / Σ n(n-1)
• What is the known conclusion for a greater species diversity index?

  Greater stability of an ecosystem.
• Why is random sampling used?

  To avoid any bias in collecting data, and to ensure that data is valid.
• What is systematic sampling and how is it carried out?

  A sampling method whereby samples are taken at regular intervals within a set area, to measure changes through a habitat.
• Describe the three quantitative measures of abundance:

  1. Density- count the abundance then divide by quadrat area.
  2. % cover- estimation of the % of a quadrat covered by a species. Counting rule- count full and half squares.
  3. Frequency- measures the number of times a species occurs in a given number of quadrats.
• How to avoid bias with quadrats:

  The position of the quadrat must be random.