Diversity, classification and variation

• Changes in DNA can arise spontaneously during replication, and any change in the base sequence or quantity of DNA is called a mutation
• A change in the base sequence of a gene can change the sequence of amino acids. Sometimes this can result in a harmful mutation, but due to the genetic code being degenerate, the amino acid sequence may not always be changed
• Types of mutation


  • Substitution
  • Deletion
• Substitution is when one nucleotide in the DNA sequence is replaced by another. The effect of the change in an amino acid depends on the role of the original amino acids in the overall shape and function of the protein. A substitution may not always be harmful as the substituted nucleotide may code in that triplet for the same amino acid
• Deletion is when a nucleotide in the DNA sequence is lost. The loss of a single nucleotide can have a significant impact as it leads to a frame shift, resulting in completely different amino acids being
• A substitution may not always be harmful as the substituted nucleotide may code in that triplet for the same amino acid
• Deletion


  A deletion event is when a nucleotide in the DNA sequence is lost. The loss of a single nucleotide can have a significant impact as it leads to a frame shift, resulting in completely different amino acids being coded for
• Crossing over of chromatids


  When pairs of chromosomes line up they can exchange some of their genetic material. Crossing over occurs when one chromosome may swap places with the same part of its homologous pair leading to a different combination of alleles on the gene
• Stages of Meiosis


  Meiosis 1 - homologous chromosomes pair up whereby crossing over at the chiasmata may take place. The cell then divides whereby each daughter cell contains one chromosome from each homologous pair. Meiosis 2 - the chromatids of each chromosome are separated producing 4 haploid daughter cells
• Genetic diversity is the total number of different alleles in the population. A population is defined as a group of individuals of the same species that live in the same place and are able to breed with one another. A species consists of more than one population. The greater the number of alleles in a population the greater the genetic diversity, and therefore the greater the chance that a population would survive a change in their habitat
• Evolution via natural selection

  There’s a variety of different phenotypes within a population. An environmental change occurs and as a result of that the selection pressure changes. Some individuals possess advantageous alleles which give them a selective advantage and allow them to survive and reproduce. The advantageous alleles are passed on to their offspring. Over time, the frequency of alleles in a population changes and this leads to evolution
• Selection is the process by which individuals that are better adapted to their environment are more likely to survive and breed. This means that they can pass on their advantageous alleles. Every living organism is subject to selection determined by the conditions in which they are living
• Selection


  Individuals better adapted to their environment are more likely to survive and breed, passing on advantageous alleles
• Every living organism is subject to selection determined by the conditions in which they are living
• Key types of selection

  • Directional Selection
  • Stabilising Selection
• Directional Selection


  Occurs when environmental conditions change, phenotypes best suited to new conditions are more likely to survive, population mean moves in the direction of these individuals
• Directional Selection


  • Bacteria being resistant to antibiotics
• Stabilising Selection


  Preserves phenotypes with successful characteristics, reduces diversity, occurs when environment remains the same
• Stabilising Selection


  • Newborn babies weights
• Niche


  Species' role within the environment, species sharing the same niche compete with each other
• The idea that better adapted species survive is the basis of natural selection
• Ways organisms are adapted to their environment

  • Anatomical adaptations
  • Behavioural adaptations
  • Physiological adaptations
• Anatomical adaptations


  • Length of the Loop of Henlé in desert mammals
• Behavioural adaptations


  • Mating calls
• Physiological adaptations


  • Regulation of blood flow through the skin
• Species are capable of breeding to produce living offspring, named using the binomial naming system with generic and specific names
• Classification


  Naming and organising organisms into groups based on their characteristics, grouped into five kingdoms: animals, plants, fungi, prokaryotes, and protoctists
• Molecular phylogeny


  Analysis of molecular differences in organisms to determine evolutionary relatedness, leading to new taxonomic groupings: Bacteria, Archaea, and Eukaryota
• The scientific community evaluates the data in the following ways: The findings are published
• Data obtained by molecular phylogeny has been accepted by scientists and gave rise to new taxonomic groupings – all organisms can be separated into one of the three domains: Bacteria, Archaea and Eukaryota
• Scientific community evaluates the data

  1. Findings are published in scientific journals and presented at scientific conferences

  2. Scientists study the evidence in a process called peer review

  3. Scientists start collecting evidence to either support or reject the suggestion
• Biodiversity


  The variety of living organisms
• Over time, the variety of life on Earth has become more extensive but is now being threatened by human activity such as deforestation
• Ways to measure biodiversity

  • Species diversity
  • Genetic diversity
  • Ecosystem diversity
• Species diversity


  The number of different species and the number of different individuals in a community
• Genetic diversity


  A measure of the genetic variation found in a particular species, the number of alleles in a gene pool
• Ecosystem diversity


  The range of different habitats
• Calculating the index of diversity (D)

  1. D = Diversity index

  2. N = total number of organisms

  3. n = total number of organisms of each species

  4. Σ = the sum of
• Agricultural ecosystems reduce biodiversity and the number of species present because humans select for particular characteristics, reducing the number of alleles and genetic diversity
• Techniques to maintain biodiversity in agriculture

  • Using hedgerows instead of fences
  • Growing different crops in the same area (intercropping)
  • Reducing the use of herbicides and pesticides
  • Preserving wetlands instead of draining for farming use