SystematicsSystematics

the study of the diversity of organisms the study of the diversity of organisms and their evolutionary relationshipsand their evolutionary relationships

TaxonomyTaxonomy – the science of naming, – the science of naming, describing, and classifying organismsdescribing, and classifying organisms

ClassificationClassification – ordering organisms – ordering organisms into groups based on their similarities into groups based on their similarities or relationshipsor relationships

Carolus Linnaeus Carolus Linnaeus developed the modern system of classificationdeveloped the modern system of classification

Binomial system of nomenclature – Linnaeus’ Binomial system of nomenclature – Linnaeus’ system of assigning each species a unique two-system of assigning each species a unique two-part namepart name

First name is the First name is the genusgenus second name is the second name is the specific epithetspecific epithet

both names must be used to identify the species – both names must be used to identify the species – scientific namescientific name

derived from Greek and Latin roots or Latin derived from Greek and Latin roots or Latin versions of the names of persons, places or versions of the names of persons, places or characteristicscharacteristics

Scientific names are recognized by all scientists all Scientific names are recognized by all scientists all over the world – common names vary by language over the world – common names vary by language and locationand location

Taxonomic Categories Taxonomic Categories

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

Taxonomic categories form a hierarchyTaxonomic categories form a hierarchy closely related species are assigned to the closely related species are assigned to the

same genussame genus closely related genera are grouped in a closely related genera are grouped in a

single familysingle family families are grouped into ordersfamilies are grouped into ordersorders are grouped into classesorders are grouped into classes classes are grouped into phylaclasses are grouped into phylaphyla are grouped into kingdomsphyla are grouped into kingdoms these groupings can be separated into these groupings can be separated into

subgroupings such as subphyla or subgroupings such as subphyla or superclasssuperclass

Six Kingdom system of classification –Eubacteria, Six Kingdom system of classification –Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Archaebacteria, Protista, Fungi, Plantae, and AnimaliaAnimalia

Some biologists use Some biologists use domainsdomains to classify the to classify the major groups of living thingsmajor groups of living things

Systematics attempts to reconstruct Systematics attempts to reconstruct evolutionary relationshipsevolutionary relationships

phylogenyphylogeny – reconstruction of evolutionary – reconstruction of evolutionary relationships of organismsrelationships of organisms

once phylogeny is established, classification once phylogeny is established, classification can then be based on common ancestrycan then be based on common ancestry

Species have various degrees of Species have various degrees of evolutionary relationship with one another evolutionary relationship with one another depending on the degree of genetic depending on the degree of genetic divergence since their populations branched divergence since their populations branched from a common ancestorfrom a common ancestor

Criteria for classificationCriteria for classification should be a reflection of evolutionary should be a reflection of evolutionary

relationships – based on common relationships – based on common ancestryancestry

Homologous structures – similarity in Homologous structures – similarity in structures derived from a common structures derived from a common ancestorancestor organisms sharing many organisms sharing many

homologous structures are homologous structures are considered to be closely relatedconsidered to be closely related

Molecular taxonomy has emerged from advances in Molecular taxonomy has emerged from advances in molecular biologymolecular biology

focuses on molecular structurefocuses on molecular structure used to compare the nucleotide sequences of nucleic used to compare the nucleotide sequences of nucleic

acids and the amino acid sequences of proteins – acids and the amino acid sequences of proteins – important tool in taxonomyimportant tool in taxonomy

greater similarities in subunit sequences indicate greater similarities in subunit sequences indicate closer evolutionary relationshipscloser evolutionary relationships the number of differences in DNA or RNA the number of differences in DNA or RNA

nucleotide sequences or in amino acid nucleotide sequences or in amino acid sequences in two groups or organisms reflect sequences in two groups or organisms reflect how much time has passed since the groups how much time has passed since the groups branched from a common ancestorbranched from a common ancestor

genes and proteins can be used as genes and proteins can be used as molecular molecular clocksclocks

systematists are currently studying:systematists are currently studying:comparisons in ribosomal RNA comparisons in ribosomal RNA structurestructure

comparisons in mitochondrial comparisons in mitochondrial DNADNA

Systematists use two main approaches to classify organisms:Systematists use two main approaches to classify organisms:

1.1. Phylogenetic systematics (cladistics) – emphasizes Phylogenetic systematics (cladistics) – emphasizes phylogeny (common ancestry)phylogeny (common ancestry)

evolutionary relationships are expressed in evolutionary relationships are expressed in branching diagrams called branching diagrams called cladogramscladograms

each branch represents the divergence of two each branch represents the divergence of two or more new groups from a common ancestor or more new groups from a common ancestor (forms a (forms a cladeclade))

cladogramcladogram is constructed is constructed from a series of dichotomiesfrom a series of dichotomies

The sequence of branching symbolizes The sequence of branching symbolizes historical chronology.historical chronology. The last ancestor The last ancestor

common to both the common to both the cat and dog families cat and dog families lived longer ago lived longer ago than the last commonthan the last commonancestor shared ancestor shared by leopards and by leopards and domestic catsdomestic cats

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