DP Biology Vocabulary (HL)- A3.2 Classification and Cladistics

Analogous trait

Trait structures which are similar because of convergent evolution. (Similar structures, different evolution, e.g. wings on a bird and wings on a fly)

Clade

a group comprised of an ancestral species plus all of the species that have evolved from the organism.

Cladistics

A phylogenetic classification system that uses shared derived characteristics and ancestry as the criterion for grouping taxa.

Cladograms

a phylogenetic tree diagram which shows groupings based on primitive and shared derived characteristics. They typically have a "root", "node" and "terminal branch" and the node represents a hypothetical common ancestor.

Convergent evolution

where species from different lineages show similar characteristics because they are subject to similar selection pressures.

Divergent evolution

a pattern of evolution where an ancestral species evolves into a number of distinct species due to exposure of different populations to different selection pressures.

Homologous trait

Traits that are shared by species with a common ancestor. These traits are similar in structure, but may have very different functions and appearances. E.g pentadactyl limbs

Classification

Assignment of organisms into categories on the basis of shared phylogeny and characteristics. It is necessary because of the immense diversity of species that exist currently and throughout natural history.

Taxonomy

The scientific study of how living things are classified. The current system utilises the following hierarchy of taxa (groupings): kingdom, phylum, class, order, family, genus and species

molecular phylogeny

Comparison of genetic base sequences or amino acid sequences, used to deduce evolutionary relationships.

Three Domains

An update to the classification system with an extra taxonomic level above kingdoms, based on rRNA Base Sequences The groups are Bacteria, Archaea, and Eukarya

Molecular clock

model that uses comparisons of DNA sequences to estimate mutation rates, phylogeny and rate of evolutionary change