15. Genetic comparisons using DNA and proteins

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Genetic comparisons using DNA and proteins

  • DNA determines the proteins/enzymes of an organism and proteins determine the features of an organism.
    • Changes in the features of an organism are due to changes in its DNA.
  • Comparing DNA and proteins of different species helps scientists to determine the evolutionary relationships between them.

Comparison of DNA base sequences

  • When one species gives rise to another during evolution, the DNA of the new species will be similiar.
  • MUTATIONS will cause the sequence of nucleotide bases in DNA of the new species to change - over time the new species will get more and more differences in its DNA.
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DNA Hybridisation

Its used to compare the DNA of 2 species.

1. DNA from 2 species is extracted, purified and cut into small pieces. DNA from one species is labelled with a radioactive/flouresent marker and mixed with the unlabelled DNA.

2. It is heated to separate the double strand. Then its cooled to allow the strands to recombine with other strands that have a complementary sequence of bases.

3. Some of the double strands will contain 1 from each species -HYBRID STRANDS

4. The hybrid strands are separated from the others and the temperature is increased in stages.

In the hybrid strand there will be more HYDROGEN BONDS linking them together. The more hydrogen bonds, the stronger it is. The stronger it is, the higher the temperature needed to separate the strands.

The higher the temp at which the hybrid strand splits, the more closely the species are related.

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Use of DNA Sequencing in Classifying Plants

A plant used to be classifed into one of 2 groups:

MONOCOTYLEDONS: single seed leaf and thin, narrow leaves.

DICOTYLEDONS: 2 seed leaves and have broad leaves.

The new classification is:

  • 565 species of flowering plants were used to represent all the known species of flowering plants.
  • For each plant, the DNA sequence of all three genes was determined.
  • The sequences for each species were compared using computer analysis.
  • A phylogenetic tree for the families of flowering plants was devised based on the DNA sequences of the species used.
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Comparison of Amino Acid Sequences in Proteins

Comparison of amino acid sequences in proteins

  • The sequence of amino acids in proteins is determined by DNA.
  • The degree of similarity in the amino acid sequence of the same protein in 2 different species will reflect how closely they are related.
  • Once the amino acid sequence for a chosen protein has been determined for 2 species, the 2 sequences are compared - count the number of similarites/differences.
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Immunological Comparisons of Proteins

Antigens of one species will respond to antibodies on proteins in the blood serum of another.

1. Serum ALBUMIN from species A is injected into species B.

2. B produces antibodies specific to all the antigen sites on the albumin from A.

3. Serum from B is mixed with the blood of species C.

4. The antibodies respond to their corresponding antigens on the albumin in the serum of C - response is a PRECIPITATE.

The greater the number of similar antigens, the more precipiate is formed and the more closely the species is related.

The fewer number of similar antigens, the less precipitate is formed and the less closely the species are related.

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Courtship Behaviour

Why is it necessary? Reproduction means a species can survive over time. Each individuals tries to ensure their DNA is passed on to the next generation. Females of most species produce eggs at a certain time, its important mating is successful nad the offspring have a chance of survival.

It enables individuals to:

  • RECOGNISE MEMBERS OF THEIR OWN SPECIES - to ensure mating only takes place between members of the same species as only members of the same species can produce fertile offspring.
  • IDENTIFY A MATE THATS CAPABLE OF BREEDING - as both partners need to be sexually mature, fertile and receptive to mating.
  • FORM A PAIR BOND - leads to successful mating and raising of offspring.
  • SYNCHRONISE MATING - takes place when theres a maximum chance of the sperm and the egg meeting.
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Courtship Behaviour

  • Females are often receptive to mating when they produce eggs.
  • Courtship behavior is used by males to determine whether a female is at this receptive stage.
    • If she responds with an appropriate behavioral response, courtships continues and is likely to result in the production of offspring.
    • If she isn't receptive, she exhibits a different pattern of behavior and the male ceases to court her.
  • During courtship, animals use signals to communicate with a potential mate and members of their own sex - males use and ACTION.
    • Acts as a stimulus to the female, who responds with an action of her own. Her response acts as a stimulus for the male to carry on.
      • STIMULUS - RESPONSE CHAIN.
  • The chain of actions is the same for all members of a species, but differs for different species - both can recognise if their partner is of the same species and they may be prepared to mate.
  • The longer the courtship sequence, the more likely mating will result.
  • If at any one point, one of the pair fails to respond appropriately, the courtship sequence ends.
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Courtship Behaviour

  • Females are often receptive to mating when they produce eggs.
  • Courtship behavior is used by males to determine whether a female is at this receptive stage.
    • If she responds with an appropriate behavioral response, courtships continues and is likely to result in the production of offspring.
    • If she isn't receptive, she exhibits a different pattern of behavior and the male ceases to court her.
  • During courtship, animals use signals to communicate with a potential mate and members of their own sex - males use and ACTION.
    • Acts as a stimulus to the female, who responds with an action of her own. Her response acts as a stimulus for the male to carry on.
      • STIMULUS - RESPONSE CHAIN.
  • The chain of actions is the same for all members of a species, but differs for different species - both can recognise if their partner is of the same species and they may be prepared to mate.
  • The longer the courtship sequence, the more likely mating will result.
  • If at any one point, one of the pair fails to respond appropriately, the courtship sequence ends.
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