D5 Phylogeny and Systematics

Question 1

Outline the value of classifying organisms

Answer 1

• Allows us to distinguish between and compare organisms
  
  • Makes it easier to identify organisms
  • Makes it easier to collect, sort and store information about organisms
  • Shows how closelyorganisms are related and suggests evolutionary links
  • Allows predictions to be made about characteristics of members of a group

Question 2

Explain the biochemical evidence provided by the universality of DNA and protein structures for the common ancestry of living organisms

Answer 2

• The genetic code is universal
  
  • All organisms use DNA and/or RNA as their genetic material
  • The same four bases are used
  • The same codons code for the same amino acids
  • All living organisms use the same 20 amino acids for protein synthesis

Question 3

Explain how variation in specific molecules can indicate phylogeny

Answer 3

• Phylogeny is tracing evolutionary links and origins by comparing similar molecules from different species
  
  • Variations in these molecules (either base or amino acid sequence) will occur due to mutations which accumulate over time
  • The greater the differences between the common molecules, the longer the time span since the two species had a common ancestor
  • Mitochondrial DNA is useful for tracing phylogeny as it is inherited via the maternal line, lacks recombination and has a known mutation rate

Question 4

Outline how biochemical variation can be used as an evolutionary clock

Answer 4

• Some genes accumulate mutations at a relatively constant rate
  
  • If this rate of change is known, scientists can calculate the time of divergence between two species based on the number of differences

Question 5

Discuss limitations of the evolutionary clock concept

Answer 5

• The rate of change can differ for different groups of organisms (e.g. animals and plants)
  
  • The rate of change can vary between different genes
  • Over long periods, earlier changes may be reversed by later changes

Question 6

Define clade

Answer 6

A group of organisms all descended from a common ancestor

Question 7

Define cladistics

Answer 7

A method of classification of living organisms based on the construction and analysis of cladograms

Question 8

Distinguish between analogous and homologous structures

Answer 8

Analogous from different ancestor (convergent evolution), homologous come from common ancestor (divergent evolution.
Analogous have similar function but different structure, homologous don’t have similar function but do have similar structure.

Question 9

Give an example of analogous characteristics

Answer 9

Wings in bats, birds, insects

Question 10

Give an example of homologous characteristics

Answer 10

Pentadactyl limb in vertebrates

Question 11

Discuss the relationship between cladograms and the classification of living organisms

Answer 11

• Classification was traditionally based on morphology (structural characteristics)
  
  • Methods used to construct cladograms typically utilise a different approach (e.g. molecular data - more objective)
  • Cladograms can show ancestral relationships and reflect how recently two groups shared a common ancestry
  • As such they should be considered a good complement to traditional classification schemes
  • In some cases, cladograms have lead to revisions in scientific classifications