4.7 Investigating diversity

• Genetic diversity within, or between species, can be made by comparing:

  • The frequency of measurable or observable characteristics
  • The base sequence of DNA
  • The base sequence of mRNA
  • The amino acid sequence of the proteins encoded by DNA and mRNA
• Methods for classifying organisms based on evolutionary relationships:

  COMPARISON OF OBSERVABLE CHARACTERISTICS

  • Each observable characteristic is determined by a gene or genes (with environmental influences)
  • The variety within a characteristic depends on the number and variety if alleles of that gene
• Methods for classifying organisms based on evolutionary relationships:

  COMPARISON OF OBSERVABLE CHARACTERISTICS - LIMITED

  • Large number of characteristics are coded for by more than one gene (polygenic) - not discrete from one another, vary continuously, so is difficult to distinguish from one another
  • Characteristics can also be modified by the environment
  • Differences may be the result of different environmental conditions rather than different alleles
• Methods for classifying organisms based on evolutionary relationships:

  • Inferring DNA differences from observable characteristics has been replaced by directly observing DNA sequences themselves
  • This has been made possible through the advances in gene technology made over recent years
• Methods for classifying organisms based on evolutionary relationships:

  COMPARISON OF DNA BASE SEQUENCES

  • Sample DNA of a species members and sequence it to produce a pattern of coloured bands
  • Analysis of these patterns allows us to compare one species with another to determine how diverse they are
• Methods for classifying organisms based on evolutionary relationships:

  COMPARISON OF DNA BASE SEQUENCES

  • The higher the percentage of similarity in the order of their base sequence, the more closely related they are
• Methods for classifying organisms based on evolutionary relationships:

  COMPARISON OF DNA BASE SEQUENCES

  • When one species gives rise to another species during evolution, the DNA of the new species. will initially be very similar to that of the species that gave rise to it
  • Due to mutations, the sequences of nucleotide bases in the DNA of the new species will change
  • Over time, the new species will accumulate more and more differences in its DNA - So expect species more closely related to show more similarity in their DNA base sequences than distantly related
• Methods for classifying organisms based on evolutionary relationships:

  COMPARISON OF BASE SEQUENCE OF mRNA

  • mRNA is coded for by DNA
  • The base sequences on mRNA are complementary to those of the strand of DNA from which they were made
  • Can measure DNA diversity, therefore genetic diversity, by comparing the base sequence of mRNA
• Methods for classifying organisms based on evolutionary relationships:

  COMPARISON OF AMINO ACID SEQUENCES IN PROTEINS

  • The sequence of amino acids in proteins is determined by mRNA which, in turn, is determined by DNA
  • Genetic diversity can therefore be measured by comparing the amino acid sequences of a species' proteins
• Methods for classifying organisms based on evolutionary relationships:

  COMPARISON OF AMINO ACID SEQUENCES IN PROTEINS

  • Once the amino acid sequence for a chosen protein has been determined for two species, the two sequences are compared
  • Count either the number of similarities or the number of differences in each sequence