3.4.7 Investigating diversity

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

  • frequency of measurable or observable characteristics
  • base sequence of DNA
  • base sequence of mRNA
  • amino acid sequence of the proteins encoded by DNA and mRNA
• The limitations of comparing the frequency of measurable or observable characteristics to investigate genetic diversity are that:

  • not precise enough if only one characteristic is looked at
  • environmental factors also have an influence on physical characteristics
  • large number of characteristics are coded for by more than one gene (polygenic)
• When comparing DNA base sequences to investigate genetic diversity:

  • DNA can be extracted from blood or skin samples from living organisms or from fossils
  • extracted DNA is processed, analysed and base sequence is obtained
  • computer used to highlight matches between DNA samples of different species
  • more similarities there are in DNA base sequence, more closely related members of the same species are
• Comparing mRNA base sequences

  • mRNA is often easier to isolate from cells than DNA as it is found in the cytoplasm and there are usually multiple copies of the same mRNA
  • collected mRNA from an individual can be used as a template to produce cDNA (complementary DNA) which is then analysed
  • unlike original DNA in nucleus, cDNA contains only exons (coding regions), and no introns.
• Comparing amino acid sequence in protein

  • proteins are often easier to isolate from cell than DNA
  • sequence of amino acids of the same protein can be compared between individuals

  Limitations:

  • amino acid sequences of proteins evolve much slower than DNA, especially if protein is of high importance
  • so protein comparisons do not provide as much information regarding evolutionary relationships as DNA/mRNA base sequence comparisons
• When measuring variation...

  • large sample size is used so it is representative of the whole population so that the data is reliable.
  • random sampling is used to reduce the possibility of bias
  • to make sure results have biological reasoning, the data is analysed with a statistical test to see if chance has influenced the data
• Random sampling

  1. divide field into a grid
  2. generate co-ordinates using a random number generator - at least 10
  3. place quadrat and take samples at each set of coordinates
• Using the mean and range has disadvantages:

  1. Range gives us the difference between the highest and lowest values and this includes extreme data that may not be representative
  2. Range may includes anomalies
  3. Comparing ranges between two sets of data doesn’t indicate whether a difference is significant
• Standard deviation is a measure of how spread out data is from the mean.
• Advantages of using standard deviation (SD):

  • Range gives us the difference between the highest and lowest values which includes extreme data that may not be representative, SD shows the spread of data about the mean
  • Range includes anomalies, SD reduces the effect of anomalies
  • Comparing ranges between two sets of data doesn’t indicate whether a difference is significant, SD can be used to indicate a significant difference
• If the standard deviation around both means do not overlap, then it is likely that there is a significant difference between them and the results are not due to chance.
• If the means of data overlap then it is likely there is no significant difference between them, and they are due to chance.
• A significant difference between two data sets means that there is a measurable difference between the groups and that, statistically, the probability of obtaining that difference by chance is very small (usually less than 5%).