Cladistics 5.4

Cladistics Practice of creating phylogenic trees based upon shared characteristics. Phylogenics is the study of evolutionary relationships between organisms.

Clades Groups of organisms that share a common ancestor. Include all the living, ancestral species, and any extinct species that came between.

Identifying Clade Members Most cladograms are constructed using molecular comparisons. The more similar a base sequence between to species, the closer they are related.

Molecular Clock Differences in base sequences between species appear due to mutation. Mutations happen at a steady rate. Scientists can look at the number of mutations between two species and reason how long ago they were similar.

Comparative Anatomy Cladograms used to be completed using comparative anatomy. Problematic due to analogous structures and homologous structures.

Analogous Structures Structures that are similar in function, but are evolved in unrelated species. Result of convergent evolution.

Homologous Structures Structures that develop from similar tissue and have same makeup, but different functions. Due to divergent evolution.

Cladograms Tree like diagrams that are based on clades. Based on parsimony, the less changes the better. Nodes are branch points that represent ancestors who split off to form 2 new species.

As you go up the cladogram, organisms develop new traits As you go up the cladogram, organisms develop new traits. These traits are called derived traits/ characteristics.

Reclassification Early clades were constructed using comparative anatomy. Clades have been redone using molecular methods.