A3.2 Classification and cladistics

Classification

The process of putting organisms into groups

Taxonomic hierarchy

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species (Dear King Philip CamE Over For Great Soup)

Taxonomy

The classification of living organisms

Benefits of taxonomy

Universal communication of biological information between scientists, predictions of characteristics of species in the same group, provide information about how a species evolved

Difficulties of the traditional classification system

Sets an arbitrary limit on the number of groupings which does not always correspond to divergence by evolution, diverging populations may be hard to distinguish

Cladistics

A method of classifying organisms into groups of species called clades

Clade

A branch in a cladogram representing a group of organisms which evolved from a common ancestor

Cladogram

A branching tree diagram that shows evolutionary relationships among organisms

Evidence for placing organisms in a clade

Similarities in DNA sequences or the amino acid sequences of proteins, similarities in the size and shape of anatomical structures

Relationship between time, evolutionary relationships, and biological sequences

Mutations accumulate gradually over long periods of time. When the number of differences in the molecular sequence of organisms is compared, the larger the number of differences, the longer since they diverged from a common ancestor

Mutation rate

The frequency at which mutations occur per nucleotide in each round of cell division

Molecular clock

With the assumption of a relatively constant mutation rate, the number of differences in the molecular sequence of organisms can be used to estimate the time since they diverged

Building cladograms

Cladograms are built by grouping organisms based on their homologous characteristics, specifically molecular sequences such as the nitrogenous bases of DNA and the amino acid sequence of proteins

Fewer differences in the base or amino acid sequences of organisms implies that

There has been less time for mutations to occur and the organisms are more closely related

More differences in the base of amino acid sequences of organisms implies that

There has been more time for mutations to occur and the organisms and less closely related

Parsimony

A principle that states that the best cladogram is the one that requires the fewest changes

Process of creating cladograms using bioinformatic tools

1. Acquire homologous sequence data

2. Alignment of sequence data

3. Building the cladogram by adding the organisms with the most similar sequence alignments

Node

The branching point that represents a hypothetical ancestor, indicating the point of divergence

Root

Located at the bottom of the cladogram and represents the common ancestor that all organisms in the cladogram share

Terminal branch (taxa)

The ends of the branches and can be individuals, groups, or species

Three domains of life

Eubacteria, archaea, and eukaryotes