The Tree of Life

Chapter 17

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17.1 Taxonomy

The science of naming

and classifying organisms

2000 years ago –

Aristotle

Grouped plants and animals

Based on structural

similarities

Greeks and Romans

included categories

Genus = Latin for group

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Taxonomy

Mid – 1700’s

Naming organisms Polynomials

Descriptive phrases

European honeybee Apis pubescens thorace

subgriseo abdomine fusco pedibus posticis glabis untrinque margine ciliatus

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Simpler System

Carl Linnaeus

Swedish biologist

Developed binomial

nomenclature

Two-part naming

system

Ex: European

honeybee

Apis mellifera

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Scientific Names

Unique two-part name for a species

Genus - First name Taxonomic category

of similar organisms

Organisms have common important characteristics

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Scientific Names

Species = Second name One specific kind of

living thing

Identifies the particular type of organism

Most specific and basic naming unit

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Rules for Scientific Names

Genus

Always first

Capitalized 1st letter

Species

Always second

NOT capitalized

Both

Italicized or underlined

Based on Latin language

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Scientific Names

Conform to rules established

No two the same

Gives biologist common way of communicating

Common names have problems Ex: Robin

Different bird in US and England!

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Classifying Organisms

Carl Linnaeus

Classification system

Ranked system of

groups

Large groups subdivided

into smaller groups

Increasingly similar

7 groups total

Now we have one

more group

= Eight group levels

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Classifying Organisms

Groups

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

Definition

Group of similar kingdoms

Group of similar phyla

Group of similar classes

Group of similar orders

Group of similar families

Group of similar genera

Group of similar species

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Classifying Organisms

Groups

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

Diverse

Similar

Biggest

Smallest

Danish Kings Play Chess On Fine Green Silk

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Identifying Organisms

Field Guides

Use:

Image

Description

General info

Range

Common name

Scientific name

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Identifying Organisms

Dichotomous Keys Use:

Pairs of descriptions

OR a question that can be answered in ONLY 2 ways

Read both descriptions or question

Choose one

Follow directions for next step

End up with a scientific name

Ex: 1a. This organism has an exoskeleton - go to number 2

1b. This organism has an endoskeleton or no skeleton - go to number 3 13

Identifying Organisms

Species

Unique

Differences in

appearance and

structure

Ex: Paramecium

syngens

Once thought to be a

single species

Look similar, but other

differences

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Species

Biological species

Defined by 1942 –

Ernst Mayr:

A group of organisms

that can reproduce

only among

themselves and are

usually contained in a

geographic region

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Hybrids

Hybrids

Offspring produced by

different species

interbreeding

Reproductive barriers

not complete

Some are fertile!

Ex: Dogs and wolves

Dogs = Canis familiaris

Wolves = Canis lupus

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Biological Species Concept

Reproduction:

Most of kingdom

Animalia = limited

Strong barriers

“Species only” fails in:

Organisms that reproduce

asexually

Ex: prokaryotes

Transfer genes

outside of

reproduction

Still working on how

to classify them

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17.2 Classification of

Species

Put into groups based on

similarities and differences

More similar = closely related

Suspect common ancestor

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Classification of Species

Similarity of structure

can be misleading

Not all

characteristics

inherited by offspring

Ex: Wings

Both birds and

insects have . . .

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Phylogeny

Evolutionary history for a group of

species

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Looking at

Structures

Convergent evolution

Converge = Come

together

When similarities develop

in organisms not closely

related b/c

Live in similar habitats thus

have similar adaptations

Analogous characters

Arise through convergent

evolution 21

Characters in Groups

Ancestral character

Feature in common

ancestor of both

groups

Ex:

Backbone

Birds and mammals

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Characters in Groups

Derived character

Found in only some

members of a group

More shared = more

closely related

Ex: Feathers

Birds but Not

mammals

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Cladistics

Classification based on common ancestry

Clade - group of species that shares a common ancestor

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Cladogram

Cladogram

Branching diagram

Shows hypothesized

evolutionary

relationships

Tips represent

groups of descendent

taxa

Nodes represent

common ancestors

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Cladistics

Outgroup – shares no derived

characters with other groups being

studied

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Cladogram

Shared derived character Evidence that groups are closely related

Ex: mammary glands

Shared ancestral characters Not evidence groups are closely related

Ex: Limbs

Classification 12 min

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Cladograms

Strengths

Objectivity

Either character exists or

doesn’t

Weakness

Each character treated

the same

Character impact or

importance ignored

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Phylogenetic Tree

Taxonomist assign

importance to

characters

Branching tree-like

diagram

Shows evolutionary

relationships

inferred

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Molecular Evidence

Uses DNA to show

relationships

Often considered the “last

word” by scientists

Usually agrees with

classification that was

based on physical

appearances

Reclassification sometimes

necessary 30

17.3 Molecular Clocks

Models that use mutation

rates to estimate

evolutionary time

Hypothesized that changes

in DNA “add up”

Rate of mutations =

“ticking” of time

More mutations = less

closely related

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Mitochondrial DNA

mtDNA

Found only in mitochondria

Only inherited from mother

Sperm loses mitochondria after fertilization

Mutation rate ~10x faster than nuclear DNA

Often used as molecular clock

Help classify closely related organisms

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Ribosomal RNA

rRNA

Useful when comparing different species

that may be very distantly related

Lots of time has passed

Lower mutation rate

Was used to reclassify Archaea and

Bacteria into different domains

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17.4 Domains and Kingdoms

Domain

Largest, broadest group

Recent classification

group

1977, Carl Woese

American

Prokaryotes differ

fundamentally in rRNA

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Domain Bacteria

Contains kingdom Bacteria

Unicellular prokaryotes

Contains autotrophs and

heterotrophs

Classified by:

Shape

Need for oxygen

Whether the cause disease

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Domain Archaea

Contain kingdom Archaea

Unicellular prokaryotes

Some autotrophic, some heterotrophic

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Domain Archaea

Cell walls do NOT contain peptidoglycan

Live in “extreme” environments

Salt lakes

Antarctic waters

Deep sea vents

Hot geysers

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Domains Archaea and

Bacteria

No true “species”

Genes are shared outside of typical

reproduction

Still trying to decide how to classify

Used to be classified together in one

kingdom: Monera

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Domain Eukarya

Includes kingdoms:

Protista

Plantae

Fungi

Animalia

Eukaryotic cells

Unicellular or multicellular

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Review of Kingdoms

Bacteria

Archae

Protista

Fungi

Plantae

Animalia

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Kingdom Bacteria

Cell wall made of

peptidoglycan

Web-like

carbohydrate

strands and

peptide bridges

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Kingdom Archaea

Cell wall

No peptidoglycan

Cell membrane

Different lipids than

bacteria or

eukaryotes

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Kingdom Protista

Many unicellular

Some have cell

walls

Heterotrophs or

autotrophs

Many move

Most reproduce

asexually

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Kingdom Fungi

Most multicellular

Except yeasts

Cell walls contain

chitin

Tough carbohydrate

Heterotrophic

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Kingdom Plantae

Multicellular

Cell walls

Cellulose (complex

carb)

Eukaryotic

Autotrophic

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Kingdom Animalia

Multicellular

Heterotrophs

Eukaryotic

Mostly diploid cells

No cell wall

Organized cells

Motility

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