Genetic information, variation and relationships

• Why is random sampling necessary?

  1. Avoid sampling bias - selection process is likely to have a degree of bias, whether done deliberately or unwittingly - may be making unrepresentative choices.
• Outline the process of random sampling

  = Taking measurements of individuals, randomly selected from the population of organisms being investigated.

  
  

  1. Divide area into grid of numbered lines.

  
  

  2. Use a computer to generate a random series of co-ordinates.

  
  

  3. Take samples at the intersections of these co-ordinates.

  
  

  NB => measurements can be relied upon if individuals sampled are representative of the population.
• Explain the balance between conservation and farming?

  1. Giving legal protection to endangered species.

  
  

  2. Creating protected areas such as SSSIs (Sites of Special Scientific Interest) and AONBs (Areas of Outstanding Natural Beauty) => restrict further development, including agricultural development.

  
  

  3. Environmental Stewardship scheme which encourages farmers to conserve biodiversity - by planting hedgerows and leaving margins around fields for vegetation to grow.
• How can agricultural practices reduce biodiversity?

  1. Woodland clearance - increases area of farmland, but directly reduces number of trees and tree species - destroying habitats, shelters and food sources.

  
  

  2. Hedgerow removal - done to increase area of farmland - reduces biodiversity and destroys habitats, shelters and food sources.

  
  

  3. Pesticides - reduces diversity as pests killed. Any predators with pests as prey will lose out.

  
  

  4. Herbicides - reduces diversity as unwanted plants / weeds killed - eliminates food source also.

  
  

  5. Monoculture - Farmers have fields containing only one type of plant ---> single type of plant reduces biodiversity directly and will support fewer organisms - either as a habitat or food source.
• Equation for Index Diversity

  
• Define Index of Diversity

  = The relationship between the number of species in a community and the number of individuals in each species
• Define Species Richness

  = A measure of the number of different species represented in an ecological community, landscape or region
• Define Biodiversity

  = The variety of plant and animal life in the world or in a particular habitat, a high level of which is usually considered to be important and desirable
• Outline how Immunological Comparisons can clarify evolutionary relationships

  - Antibodies of one species will respond to specific antigens on proteins, such as albumin, in the blood serum of another.

  
  

  1. Serum albumin from species A injected into B.

  
  

  2. Species B produces antibodies specific to all antigen sites on species A's albumin.

  
  

  3. Serum extracted from species B, containing antibodies specific to the antigens on the species A albumin.

  
  

  4. Serum from species B mixed with serum from species C blood.

  
  

  5. Antibodies respond to their corresponding antigens on albumin in series of species C.

  
  

  6. Number of similar antigens ---> more precipitate formed ---> more closely-related species.
• Outline how Amino Acid Sequencing can clarify evolutionary relationships

  1. Proteins made of amino acids ---> sequence of amino acids in a protein is coded for by the DNA base sequence.

  
  

  2. Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins.

  
  

  3. Cytochrome C, for example. The more similar the amino acid sequence of cytochrome C in two different species ---> more closely related species are likely to be.
• Outline how Genome Sequencing can clarify evolutionary relationships

  1. Entire base sequence of DNA can be determined (due to GS advances).

  
  

  2. DNA base sequence of one organism can be compared to DNA base sequence of another organism to see how closely related they are.

  
  

  => closely related species will have a higher % of similarity in their DNA base sequence.

  
  

  => can clarify evolutionary relationships - can compare DNA base sequences of one organism with others in same family (for example) ---> if significantly different then can be reclassified.
• List the 3 ways in which advances in technologies/techniques can clarify evolutionary relationships.

  1. Genome sequencing.

  
  

  2. Comparing amino acid sequence.

  
  

  3. Immunological comparisons.

  
  

  4. Similarities in COURTSHIP BEHAVIOURS
• What is courtship behaviour?

  = Set of species-specific display behaviours in which an animal attempts to attract a mate of the same species and exhibit their desire to copulate.
• Outline the taxa hierarchy

  Domain

  Kingdom

  Phylum

  Class

  Order

  Family

  Genus

  Species
• What are the 8 taxa? How are they arranged?

  Taxa = hierarchal levels of groups used to classify organisms.

  
  

  Domain

  Kingdom

  Phylum

  Class

  Order

  Family

  Genus

  Species

  
  

  = Arranged in a hierarchy, with the largest groups on top.

  
  

  = Organisms can only belong to one organism in the group at each level in the hierarchy - no overlap.
• Define Taxonomy

  = Science of classification - involves naming organisms and organising them into groups.
• Define Phylogeny


  = Study of evolutionary history of groups of organisms.

  
  

  => tells which organisms are related to each other and how closely related they are.
• What are the types of adaptations of natural selection?

  Anatomical - Structural features e.g layer of blubber

  Physiological - Processes inside body e.g. hibernation lowers rate of metabolism

  Behavioural - Way an organism acts e.g. possums playing dead
• What is the result of natural selection?

  Results in species better adapted to the environment in which they live.
• Outline an example of stabilising selection

  - Human birth weights:

  
  

  1. Infant mortality rate lowest in range 2.5-4.0 kg and increases either side of this range.

  
  

  2. Mortality rate is greater at the two extremes => population's characteristics are being preserved rather than changed ---> phenotypes around the mean of the population selected for and those at both extremes selected against.
• Define stabilising selection

  = Selection favouring individuals with the average characteristic of the population.

  
  

  => preserves overall characteristics of the population.
• Outline an example of directional selection

  - Antibiotic resistance with penicillin:

  
  

  1. Spontaneous mutation in allele of a gene in a bacterium ---> new protein (enzyme - penicillinase) produced.

  
  

  2. Bacterium in situation where penicillin being used to treat an individual (by chance) ---> mutation gives bacterium an advantage as it can produce penicillinase and survive.

  
  

  3. Surviving bacterium divides by binary fission ---> small population of resistant bacteria forms.

  
  

  4. Population of resistant bacteria grows at expense of non-resistant population

  => allele frequency of penicillinase allele increases in the population.

  
  

  => normal distribution curve shifts in direction of higher penicillin resistance.

  
  

  => antibiotic use places a directional selection pressure on the bacterial population.
• Define directional selection

  = Selection favouring individuals that vary in one direction from the mean of the population.

  
  

  => changes overall characteristics in the population.
• Define selection

  = Process by which organisms better adapted to their environment are more likely to survive and reproduce.
• What factors cause genetic diversity?

  - Gene mutation

  - Chromosome mutation

  - Random factors associated with meiosis and fertilisation
• Define populations

  = Group of organisms of the same species in a particular habitat at one time.
• What is the founder effect? Give an example.

  When just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool

  e.g. Amish people ( Swiss --> NA)
• Explain what reduces genetic diversity

  Genetic bottleneck - reduces number of different alleles
• What increases genetic diversity within a population

  Mutations in the DNA

  Different alleles being introduced into a population from another population ( migration)
• Define genetic diversity


  Number of different alles of genes in a population
• Why is crossing over so important?

  Without crossing over and recombination, only 2 genetically different types of daughter cell would be produced => crossing over increases genetic variation even further.
• How does crossing over lead to more genetic variation?

  1. Each chromosome lines up alongside homologous partner in meiosis I.

  
  

  2. Chromatids of each pair twist around each other.

  
  

  3. Tensions created (due to twisting) + portions of chromatids break off.

  
  

  4. Broken portions might then rejoin with the chromatids of its homologous partner => recombination.

  
  

  5. Usually equivalent portions (same genes) of homologous chromosomes that are exchanged.

  
  

  6. New genetic combinations of maternal and paternal alleles produced.
• What factors of meiosis will lead to genetic variation?

  1. Independent segregation of homologous chromosomes.

  
  

  2. Genetic combination by crossing over.

  
  

  3. Haploid gametes fuse randomly at fertilisation

  ---> produces more genetic variation in offspring.

  
  

  4. Gametes usually come from different parents

  ---> 2 different genetic makeups combined so even more variety as a result.
• Define Reduction Division

  = The number of chromosomes in each gamete is reduced to half of the original number

  
  

  Diploid --> Haploid
• Why do we half the chromosome number in meiosis?

  1. To produce haploid gametes ---> so zygote and offspring formed have the correct diploid number of chromosomes as haploid gametes from mother and father fuse together, restoring diploid number of chromosomes.

  
  

  2. Ensures one allele from each of mother and father for each gene.

  
  

  => maintains a constant number of chromosomes in adult species.
• Outline a diagram showing the chromosome content of the cells after the first and second meiotic division

  
• Outline the process of Meiosis II

  1. Chromatids are separated by a further division into 4 cells, each with a single chromatid.
• Outline the process of Meiosis I

  1. Homologous chromosomes pair up and their chromatids wrap around each other.

  
  

  2. Equivalent portions of chromatids can be exchanged in crossing-over.

  
  

  3. Homologous chromosomes separate, with one chromosome from each pair going to each of two daughter cells.
• What happens pre-meiosis?

  INTERPHASE: ach chromosome replicates to form a new genetically identical chromatid. The sister chromatids are held together by the centromere.
• How does meiosis differ from mitosis?

  Meiosis = 4 genetically different haploid daughter cells.

  Mitosis = 2 genetically identical diploid daughter cells.