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