Cladistics

Topic 5.4

Essential idea: The ancestry of groups of species can be deduced by comparing their base or amino acid sequences.

Understandings

5.4.U1 A class is a group of organisms that have evolved from a common ancestor

Clade diagram

5.4.U2 Evidence for which species are part of the class can be obtained from the base sequences of a gene or the                      corresponding amino acid sequence of protein

Evidence of clade

5.4.U3 Sequence differences accumulate gradually so there is a positive correlation between the number of differences                      between two species in the time since they diverged from a common ancestor

Correlation between nucleotide substitution and species divergence

5.4.U4 Traits can be analogous or homologous

Comparison of analogous and homologous traits

5.4.U5 Cladograms are trees that show the most probable sequence divergence in clades

Cladogram and divergence

5.4.U6 Evidence from cladistics has shown that classification of groups based on structure do not correspond the evolutionary                      origins of the group or species

Place mouse on figure to view relationship between jellyfish, starfish and human.

Evidence for reclassification

Applications

5.4.A1 Cladograms including humans and other primates

Cladogram of humans and other primates

5.4.A2 Reclassification of the figwort family using evidence from cladistics

Monophyletic and polyphyletic clades of figwort family
Explanation of figwort family reclassification

Skills

5.4.S1 Analysis of cladograms to deduce evolutionary relationships

Click on Go to Cladogram Analysis to go to webpage to practice deducing evolutionary relationships

Go to Cladogram Analysis
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