CHAPTER 17 – CLASSIFICATION OF ORGANISMS

17-1: Biodiversity17-2: Systematics

17-3: Modern Classification

17-1: BIODIVERSITY Biologists have named and classified almost

2 million species

Over time, scientists have created various systems of classification to organize their knowledge of the tremendous # of species

each system places species into categories based on particular characteristics

CLASSIFYING ORGANISMS

Biodiversity The variety of organisms

considered at all levels from populations to ecosystems

Terry Erwin (1980s) Catalogued insect species

in tropical rain forest Found over 1000 species in

only 19 trees

CLASSIFYING ORGANISMS Every year, biologists

discover 1000s of new species and seek to classify them in a meaningful way Ex. – the pangolin

Grouped with lizards + crocodiles due to scales?

Grouped with animals that use sticky tongues to eat ants?

TAXONOMY

Taxonomy The science of

describing, naming, + classifying organisms

Taxon Any particular

group within a taxonomic system

TAXONOMY Aristotle

Classified organisms in 2 taxa:

Plants Grouped them

based on stem differences

Animals Grouped them

based on where they lived:

Land, water, or air

TAXONOMY

Aristotle’s system was inadequate

Common names were not useful either Ex. Robin or Fir tree

Vary from place to place

More than one common name

Don’t accurately define a species (i.e. Jellyfish)

THE LINNAEAN SYSTEM Carolus Linnaeus

System that grouped organisms into hierarchical categories according to their form + structure (morphology)

System had 7 levels

LEVELS OF CLASSIFICATION Kingdom Phylum

Class Order Family Genus

Species

BINOMIAL NOMENCLATURE

Linnaeus gave an organism a species name, or scientific name, with two parts: Genus Species identifier

Examples: Homo sapiens Thamnophis melanogaster Drosophila melanogaster

Binomial nomenclature

YOUR CLASSIFICATION

Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Mammalia Order Primates Family Hominidae Genus Homo Species sapiens

BINOMIAL NOMENCLATURE Subspecies

Species that live in different geographic areas

Example: Terrapene carolina triungui

CLASSIFICATION VIDEO

17-2: SYSTEMATICS Modern biologists consider not only the VISIBLE

SIMILARITIES but also similarities in: Embryos Chromosomes Proteins DNA

Systematics Goal is to classify organisms in terms of their natural

relationships organize in context of evolution

PHYLOGENETICS

Systematic taxonomists agree that an organism’s classification should reflect PHYLOGENY (evolutionary history)

Phylogenetics The analysis of the

evolutionary or ancestral relationships among taxa.

PHYLOGENETICS Use comparisons to classify:

Living species vs. fossils Embryonic development + gene

expression Chromosomes or macromolecules

(DNA/RNA)

PHYLOGENETICS Represent

hypotheses by a phylogenetic tree (diagram) Branching pattern

indicates how closely related a subset of taxa are thought to be

May be revised with new discoveries or evidence

EVIDENCE OF SHARED ANCESTRY Biologists use fossils as important clues for the

timing of evolutionary changes + divergence The fossil record my lack evidence… May also compare…

Homologous features (jaws of pangolin + dogs) Analogous features (scales of snakes + pangolin) Embryology (amnion)

The greater the # of features shared by organisms, the more closely related the organisms are

CLADISTICS 1966 – Willi Hennig

Cladistics A system of phylogenetic

analysis that uses shared + derived characters as the only criteria for grouping taxa

Shared – feature that all members of a group have in common

Ex. Hair in mammals or feathers in birds

Derived – feature that evolved only within the group

CLADISTICS

Cladistics assume that organisms share one or more derived characters Probably inherited them from an common

ancestor Group known as a “clade”

Includes its ancestors + all descendants No other categories (i.e. order, class,

etc..) Creates a cladogram to show their

hypothesis

EXAMPLE - A CLADOGRAM

CONSTRUCTING A CLADOGRAM Out-group

Organism that is only distantly related to the other organisms

Acts as a starting point for comparisons

MOLECULAR CLADISTICS Biologist can count the shared, derived

amino acids at each position in a protein to make a cladogram

MOLECULAR CLADISTICS “Molecular Clock”

A tool for estimating the sequence of past evolutionary events

Suggests that the greater the differences between a pair of sequences, the longer ago those two sequences diverged from a common ancestor

CHROMOSOMES If two species have the same banding pattern in

regions of similar chromosomes, the regions are likely to have been inherited from a single chromosome in the last common ancestor of the two species

PUTTING IT ALL TOGETHER To classify an organism and represent its

systematics in an evolutionary context, biologists use many types of information to build and revise phylogenetic models: Physical features Embryos Genes in nucleus Mitochondrial DNA Ribosomal RNA

17-3: MODERN CLASSIFICATION Taxonomists have revised two

Linnaean-inspired categories Domains Kingdoms

THE TREE OF LIFE

Based on cell types, scientists can divide all life into two groups: Eukaryotes Prokaryotes

Carl Woese - 1977 Proposed major revision of 6 kingdom

system Compared rRNA sequences of different

organisms and grouped them according to their similarities

THREE DOMAINS OF LIFE

Insights from rRNA analyses:1. Data is consistent with hypotheses that all

living organisms inherited their rRNA genes from ancient organisms or form of life

2. All living things can be grouped into 1 of the 3 domains: BACTERIA, ARCHAEA, or EUKARYA

3. Species in domain ARCHAEA are greatly different than bacteria

DOMAIN BACTERIA

Small, single-celled prokaryotes

Have cell walls Contain peptidoglycan

Reproduce by binary fission

One circular chromosome

DOMAIN ARCHAEA Have distinctive cell membranes

Made of hydrocarbons, not fatty acids Some are autotrophic (chemosynthesis) May inhabit harsh environments

DOMAIN EUKARYA

Consists of eukaryotic organisms Includes plants, animals, fungi, + some

single-celled organisms

SIX KINGDOMS

The 6 kingdoms are more of a traditional taxonomic system

Kingdoms: Eubacteria Archaebacteria Protista Fungi Plantae Animalia