Evidence for relationships between organisms - Chapter 15 AQA AS Biology

Chapter 15 - AQA AS Biology

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  • Created by: H.N
  • Created on: 01-01-13 19:52
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  • Evidence for relationships between organisms
    • Genetic comparisons using DNA + Proteins
      • Use of DNA base sequencing in classifying plants
        • used to be based on the appearance of a plant - flowering plants placed into 2 groups
          • monocotyledons - single seed leaf, thin, narrow leaves
        • Now - based upon the DNA sequence of 3 genes found in all plants
          • sequences for each species compared using computer analysis
            • Phylogenetic tree for the families of flowering plants was devised
      • comparison of amino acid sequences in proteins
        • sequence of a.a. determined by DNA - similarity in a.a. sequence of the same protein 2 species will reflect how closely related they are
          • 2 sequences compared by either counting the no. of similarities or counting the no. of differences
        • Immunological comparison of proteins
          • principle: antibodies of 1 species will respond to specific antigens on proteins, in the blood serum of another
          • Occurs as follows:
    • Courtship behaviour
      • why is it necessary?
        • organisms need to reproduce in order for a species to survive over time
        • females of most species only produce eggs at specific times of the year - so it's important to ensure successful mating + that offspring have the max. chance of surviving
      • What it entails
        • Form a pair bond
          • leads to successful mating + raising of offspring
        • Synchronise mating
          • ensures it takes place when there is max. probability of the sperm + egg meeting
      • males use courtship behaviour to determine whether females are at the receptive stage
        • if female responds with appropriate behavioural response  courtship continues + results in production of offspring
        • If female exhibits different pattern of behaviour, male ceases to court her
      • animals use signals to communicate with a potential mate + members of their own sex
        • males usually  carry  out an action which acts as a stimulus to the female - who responds with her own action
          • continues in a STIMULUS- RESPONSE chain
            • Same for members of the same species, different for members of different species
            • The longer the courtship sequence continues, the more likely mating will occur
              • If at  any point, 1 of the pair fails to respond appropriately, the courtship sequence ends
  • Comparison of DNA base sequences
    • Genetic comparisons using DNA + Proteins
      • Use of DNA base sequencing in classifying plants
        • used to be based on the appearance of a plant - flowering plants placed into 2 groups
          • monocotyledons - single seed leaf, thin, narrow leaves
        • Now - based upon the DNA sequence of 3 genes found in all plants
          • sequences for each species compared using computer analysis
            • Phylogenetic tree for the families of flowering plants was devised
      • comparison of amino acid sequences in proteins
        • sequence of a.a. determined by DNA - similarity in a.a. sequence of the same protein 2 species will reflect how closely related they are
          • 2 sequences compared by either counting the no. of similarities or counting the no. of differences
        • Immunological comparison of proteins
          • principle: antibodies of 1 species will respond to specific antigens on proteins, in the blood serum of another
          • Occurs as follows:
    • DNA Hybridisation
      • depends upon a property of the DNA double helix
      • DNA heated - double strand seperates
        • When cooled - complementary bases on each strand recombine to reform orignial strand
      • Occurs as follows:
        • 1) DNA from 2 species is extracted, purified + cut into short pieces
          • 2) DNA from 1 species labelled by attaching a radioactive/fluorescent marker. Then mixed with unlabelled DNA of other species
            • 3) mixture of  both sets of DNA is heated to separate their strands
              • 4) mixture cooled + allowed to recombine
                • 5)  some of the double strands that reform will be made up of 1 strand from each species = HYBRIDISATION (new strands = hybrid strands)
                  • Identified because 50% labelled
                  • 6) hybrid strands separated out + temp. increased in stages
                    • 7) if species are closely related they will share many complementary nucleotide bases. Therefore more H bonds linking them
                      • The greater the no, of H bonds, the stronger the hybrid strand + the higher the temp. needed to separate into 2 single strands
                      • 8) Higher the temp. which the hybrid strand splits, the more closely related, so the lower the temp. the more distantly the species are related
  • When cooled - complementary bases on each strand recombine to reform orignial strand
  • dicotyledons - 2 seed leaves, broad leaves

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