CHAPTER 18 CLASSIFICATION

SECTION 1 FINDING ORDER IN DIVERSITY

KEY CONCEPT QUESTIONS:

How are living things organized for study?

What is binomial nomenclature? What is Linnaeus’s system of

classification?

How are living things organized for study?To study the diversity of life,

biologists use a classification system to name organisms and group them in a logical manner

TAXONOMY discipline of classifying organisms

and assigning each organism a universally accepted name

Classification

System to organize all living creaturesplantsanimalsmicrobesetc.

Why do you classify anything? to be certain everyone is talking about

the same thing Using common names can be

confusing In the United Kingdom, the word

buzzard refers to a hawk, whereas in many parts of the United States, buzzard refers to a vulture.

Woodchuck and ground hog are the same animal

Why not use common names?

Misleading starfish dragonfly

Confusing blue jay, blue coat,

corn thief dog, perro, chien

I swim,but I’m still

a bird!

Why not use common names?

But they all have only one scientific name!

Cyanocitta cristata

Pyrrhosoma nymphula

Pisaster ochraceus

A more universal way of scientifically classifying came about

BINOMIAL NOMENCLATURE classification system in which each

species is assigned a two-part scientific name

Carolus Linnaeus

The Linnean system proposed in 1700seach species has a

2 part namegenusspecies

Homo sapiens

Latin binomial

2 part scientific name Genus — larger group to which organism

belongs always capitalized

species — specific name for that organism always lowercase

example: Linnaeus named humans Homo sapiens means “wise man”

— perhaps in a show of hope & optimism

The grizzly bear is called Ursus arctos. The first part of the scientific name

—in this case, Ursus—is the genus to which the organism belongs

The second part of a scientific name—in this case, arctos—is unique to each species within the genus (this is usually a Latin name)

GENUS a group of closely related species

Linnaeus’s System of Classification TAXON

a group or level of organization; aka: taxonomic category

Genus groupings

Classify organisms into broader groups

Species that are closely related are grouped into the same genusLeopard Panthera pardusAfrican lion Panthera leoTiger Panthera tigris

Classification

Kingdom Phylum Class Order Family Genus species

Orders & families

KEY CONCEPT QUESTIONS:

How are living things organized for study?Taxonomic categories

What is binomial nomenclature?2-part universal naming system

What is Linnaeus’s system of classification?each species has a 2 part name

genusspecies

SECTION 2 MODERN EVOLUTIONARY

CLASSIFICATION

KEY CONCEPT QUESTIONS:

How are evolutionary relationships important in classification?

How can DNA and RNA help scientists determine evolutionary relationships?

Darwin's ideas about descent with modification have given rise to the study of PHYLOGENY, or evolutionary relationships among organisms.evolutionary history of a species based on common ancestries inferred

from fossil recordmorphological & biochemical

resemblancesmolecular evidence

With the help of newer technology scientists have found more accurate ways of classifying organisms

Biologists now group organisms into categories that represent lines of evolutionary descent, not just physical similarities. In other words, species placed within the

same genus should be more closely related to one another than to species of any other genus

EVOLUTIONARY CLASSIFICATION method of grouping organisms

together according to their evolutionary history

To refine the process of evolutionary classification, many biologists now prefer a method called cladistic analysis

Cladistic analysis identifies and considers only those characteristics of organisms that are evolutionary innovations—new characteristics that arise as lineages evolve over time. Characteristics that appear in recent parts of a lineage but not in its older members are called DERIVED CHARACTERS.

Illustrating phylogeny Cladograms

patterns of shared characteristics diagram that shows the evolutionary

relationships among a group of organisms

Classify organisms according to the order in time at which branches arise along a phylogenetic tree

How is a cladogram constructed?

Procedure : pg. 453 in textbook Identify the organism in the table that is least

closely related to the others. Use the information in the table to construct

a cladogram of these animals.

Analyze and Conclude:  What trait separates the least closely

related organism from the other animals?

Lack of backbone List the animals in your cladogram in

order of distance from the least closely related organism.

Trout, lizard, and human

Does your cladogram indicate that lizards and humans share a more recent common ancestor than either does with an earthworm? Explain.

Yes, lizards and humans shared an ancestor that had legs and a backbone and that evolved after the earthworm’s lineage branched off on another evolutionary pathway

Where would you insert a frog if you added it to the cladogram? Explain your answer

A frog would occupy a branch between the trout and the lizard, because it has the derived characteristic of legs. Another derived characteristic, such as dry skin, would then have to be added for the lizard.

How are genes used to help scientists classify organisms? The genes of many organisms show

important similarities at the molecular level.

The similarities can be used to help determine classification

Scientists compare the DNA of different organisms to establish similarities between them and reconstruct possible evolutionary relationships

Of Mice and Men… Evolving genomes

now that we can compare the entire genomes of different organisms, we find… humans & mice have 99% of their genes in

common 50% of human genes have a close match with

those of yeast!the simplest eukaryote

The more similar the DNA sequences of two species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms

Comparisons of DNA can also be used to mark the passage of evolutionary time.

A model known as a MOLECULAR CLOCK uses DNA comparisons to estimate the length of time that two species have been evolving independently. To understand molecular clocks, think about

a pendulum clock. It marks time with a periodically swinging pendulum.

A molecular clock also relies on a repeating process to mark time—mutation.

Molecular clocks

•Trace variations in genomes to date evolutionary changes

•Rate of change is calculated and then extrapolate back

HIV-1M samples were collected from patients between early 1980s & late 1990s. The gene evolved at a relatively constant rate. Concluded that HIV-1M strain first infected humans in 1930s.

Simple mutations occur all the time, causing slight changes in the structure of DNA

Some mutations have a major positive or negative effect on an organism's phenotype.

These mutations are under powerful pressure from natural selection.

Other mutations have no effects on phenotype. These neutral mutations accumulate in the DNA of different species at about the same rate.

A comparison of such DNA sequences in two species can reveal how dissimilar the genes are.

The degree of dissimilarity is, in turn, an indication of how long ago the two species shared a common ancestor.

Evaluating molecular homologies

Aligning DNA sequencesmore bases

in common = more closely related

analyzed by software

beware of molecular homologies

Modern Systematics

Shaking up some trees!

Crocodiles are now thought to be closer to birds than other reptiles

KEY CONCEPT QUESTIONS: How are evolutionary relationships important in

classification? evolutionary history of a species based on

common ancestries inferred from fossil record morphological & biochemical resemblances molecular evidence

How can DNA and RNA help scientists determine evolutionary relationships? The more similar the DNA sequences of two

species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms

SECTION 3 KINGDOMS AND DOMAINS

KEY CONCEPT QUESTIONS:

What are the six kingdoms of life as they are now identified? 

What is the three-domain system of classification?

Since Linnaeus’s time kingdom classification has changed.he had two kingdoms – plantae

and animalianow there are six

eubacteria, archaebacteria, protista, fungi, plantae, and animalia

There is also a level higher than kingdom called Domains

The three domains are: Bacteria

kingdom Eubacteria Archaea

kingdom Archaebacteria Eukarya

Kingdom protists, fungi, plants, and animals.

Universal Tree of Life

3 DomainsBacteriaEukaryaArchaea

KEY CONCEPT QUESTIONS:

What are the six kingdoms of life as they are now identified?  eubacteria, archaebacteria, protista,

fungi, plantae, and animalia What is the three-domain system of

classification?BacteriaArcheaEukarya