Topic 5.4 Cladistics

Question 1

Clades

Answer 1

Cladistics involve classifying organism into groups of species (clades). A clade consists of a single common ancestor and all descendants.

Cladograms are tree diagrams where each branch point represents the splitting of two new species groups from a common ancestral species. Each branch point (node) represents speciation event. The more nodes between groups the less related the groups are.

Question 2

Structural evidence

Answer 2

Historically cladograms have been constructed based on structural characteristics, however this is not always a reliable method for establishing evolutionary connections.

Related species may have distinctive (homologous) features
Unrelated species may have similar (analogous feature)

Question 3

Molecular Evidence

Answer 3

Cladograms are now being generated via a comparison of biochemical evidence (i.e. DNA or amino acid sequence similarities)

Related species will have sequences with more similarities. Amino acid sequence will accumulate differences at a slower rate to DNA sequences (due to degeneracy)

If a sequence accumulates mutations at a constant rate, the time of divergence can be calculates based on the number of mutation between two species (molecular clock)