1. Systematics
the study of the diversity of organisms and their evolutionary relationships
Taxonomy – the science of naming, describing, and classifying organisms
Classification – ordering organisms into groups based on their similarities or relationships

2. Carolus Linnaeus developed the modern system of classification
Binomial system of nomenclature – Linnaeus’ system of assigning each species a unique two-part name
First name is the genus
second name is the specific epithet
both names must be used to identify the species – scientific name
derived from Greek and Latin roots or Latin versions of the names of persons, places or characteristics
Scientific names are recognized by all scientists all over the world – common names vary by language and location

3. Taxonomic Categories
Taxon – a formal grouping of organisms at any given level (ex. species, genus, phylum – class Mammalia is a taxon)

4. Taxonomic categories form a hierarchy
closely related species are assigned to the same genus
closely related genera are grouped in a single family
families are grouped into orders
orders are grouped into classes
classes are grouped into phyla
phyla are grouped into kingdoms
these groupings can be separated into subgroupings such as subphyla or superclass

5. Six Kingdom system of classification –Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia

6. Some biologists use domains to classify the major groups of living things

7. Systematics attempts to reconstruct evolutionary relationships
phylogeny – reconstruction of evolutionary relationships of organisms
once phylogeny is established, classification can then be based on common ancestry
Species have various degrees of evolutionary relationship with one another depending on the degree of genetic divergence since their populations branched from a common ancestor

8. Criteria for classification
should be a reflection of evolutionary relationships – based on common ancestry
Homologous structures – similarity in structures derived from a common ancestor
organisms sharing many homologous structures are considered to be closely related

9. Molecular taxonomy has emerged from advances in molecular biology
focuses on molecular structure
used to compare the nucleotide sequences of nucleic acids and the amino acid sequences of proteins – important tool in taxonomy
greater similarities in subunit sequences indicate closer evolutionary relationships
the number of differences in DNA or RNA nucleotide sequences or in amino acid sequences in two groups or organisms reflect how much time has passed since the groups branched from a common ancestor
genes and proteins can be used as molecular clocks

10. systematists are currently studying:
comparisons in ribosomal RNA structure
comparisons in mitochondrial DNA

11. Systematists use two main approaches to classify organisms:
1. Phylogenetic systematics (cladistics) – emphasizes phylogeny (common ancestry)
evolutionary relationships are expressed in branching diagrams called cladograms
each branch represents the divergence of two or more new groups from a common ancestor (forms a clade)
cladogram is constructed from a series of dichotomies

12. The sequence of branching symbolizes historical chronology.
The last ancestor common to both the cat and dog families lived longer ago than the last common ancestor shared by leopards and domestic cats

14. Classical evolutionary taxonomy – uses a system of phylogenetic classification and presents evolutionary relationships in phylogenetic trees