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Organizing Information About Species
CHAPTER 19
AP Biology
Spring 2011
Taxonomy and Cladistics
CHAPTER 19.1
A Rose by Any Other Name…
 Taxonomy is the
science of naming
and classifying
species
 Early taxonomy had
few rules and led to
many variations in
English and Latin
naming
Carolus Linnaeus
 Developed a binomial nomenclature based
on an organism’s genus and species
 This is an organism’s unique scientific name
Carolus Linnaeus
 Linnaeus eventually used more exhaustive
categories, or taxa, to organize species
 The categories included in order from least to
most specific are:
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Domain
Kingdom
Plylum
Class
Order
Family
Genus
Species
Do Kings Play Chess Or
Farm Giant Shrimp?
Carolus Linnaeus
 Assignment into a taxon is based on shared
similarity
Ranking Versus Grouping
 Linnaeus developed his taxonomy before
knowledge of evolution
 Knowledge of evolution makes classification
more difficult
Ranking Versus Grouping
 Speciation does not happen at a distinct time
 Interbreeding may occur during speciation, or
distinct populations may interbreed after
diverging
Ranking Versus Grouping
 Phylogeny takes evolutionary patterns into
account when charting biological diversity
 Central question in phylogeny is “who is
related to whom?”
Ranking Versus Grouping
 Cladistics: one phylogenic method that
separates species in to clades (branches)
based on shared characteristics like physical,
behavioral, physiological, or molecular
features
Ranking Versus Grouping
 Because organisms have many different
characters, groupings will differ based on
what type of character is used
 The result of cladistic analysis is a cladogram,
a diagram that shows a network of
evolutionary analysis
 Cladograms represent data-based
hypotheses about species relationships and
are pliable based on new or emerging
evidence
Comparing Body Form and Function
CHAPTER 19.2
Comparative Morphology
 Comparative
morphology:
focuses on the
comparative study of
body form and
structure in different
organisms
Morphological Divergence
 Populations of a species have diverged when
gene flow between them has ceased
 Eventually common morphological traits will
also diverge
 However, the changes often represent some
homology within a lineage
Morphological Divergence
 Morphological divergence is a
macroevolutionary pattern where some
morphological homology is retained
 Vertebrate forelimbs provide an example
Morphological Divergence
 Fossilized evidence shows all land vertebrates
have a common ancestor that crouched low
on the ground and walked on all four legs
 This stem reptile had a 5-toe limb that was a
adapted into many different land vertebrate
lineages that include flight in bats and birds,
fins in penguins and dolphins, and
degeneration in snakes
Morphological Divergence
 Even though the vertebrate forelimbs are
different in size, shape, and function, it is
clear that they are alike in positioning and
structure of the bony elements
 Comparisons of early embryos show
resemblance in the bony development.
These similarities are evidence of shared
ancestry.
Morphological Convergence
 Similar body parts may emerge separately
from different lineages
 This is morphological convergence
Morphological Convergence
 In this scenario, analogous structures
emerge, and while the structures have the
same features, they have different
evolutionary lineages
 Wings provide an example of this convergent
evolution
Morphological Convergence
 Wing use is all governed by the same physical
constraints that govern flight
 Birds and bats have homologous forelimbs,
but the wing is a thin membranous
extensions of the skin
 Bird wings are lined with feathers that are
extensions derived from skin
 Insect wings develop as fused sacs that
flatten and strengthened with chitin
 Instead of developing around a forelimb
Morphological Convergence
 Analogous structures (morphological
convergence) are adaptations that emerge
after the divergence of the species
Comparing Patterns of Development
CHAPTER 19.3
Embryo Development
 Embryo development is guided by a set of
master genes
 Some master genes called homeotic genes
are responsible for shaping the developing
embryo
 Mutations in homeotic genes will have a
dramatic effect on the final shape of the
organism
Similar Genes in Plants
 Mutations to a floral identity gene have a
dramatic effect on plant morphology
 Consider Apetela 1:
 In wild cabbage, Apetela 1 mutation causes
mutant flowers
 In common wall cress, Apetela 1 leads to no flower
petals
 Apetela 1 mutations affect a wide range of plant
lineages
Developmental Comparisons in
Animals
 How many legs?
 All vertebrates go through similar stages in
development
 Changes in adult body plans can be attributed to
mutations in onset, rate, or completion of early
development
 Dlx is a homeotic gene that causes limb bud
formations
 Hox is a master gene that suppresses Dlx
Developmental Comparisons in
Animals
 How many legs cont.
 In pythons, Hox is expressed along the length of
the embryo; limb buds form but do not develop
into legs
 Dlx/Hox regulation may be responsible for
variations in number and position of limbs in
mature animals
Forever Young
 Skull development in humans and
chimpanzees shows evidence of relationship
 Juvenile skulls for humans and chimps are
identical in proportion
 The skull morphology changes in later
development with human adult skulls more
closely resembling a juvenile chimp skull
Comparing DNA and Protein
CHAPTER 19.4
DNA and Proteins
 All lineages have a mix of ancestral and novel
characters including biochemical traits
observed in DNA sequence and protein
structure
DNA and Proteins
 Mutation is random and can occur anywhere
in the DNA
 Most mutations are neutral, that is they have
little or no effect on a individual’s
reproduction or survival
 Neutral mutations help to identify when
lineages diverge; more closely related species
will have more similar mutations compared
to lesser relationships
DNA and Proteins
 Further evidence of common lineage can be
found by correlating changes in the DNA with
morphological changes in the fossil record
 Biochemical comparisons by DNA sequencing
and footprinting have become faster and
more accurate with new technologies
 The field of comparative genomics deals with
these types of comparisons
Molecular Comparisons
 Comparisons of amino acid sequences can be
used to determine species relationships
 The more identical the protein sequence, the
more related the species
Molecular Comparisons
 Some essential genes have not changed
much over time due to their utility.
 Take cytochrome b for example
 Cytochrome b is essential for electron transfer
chains to function properly
 The structure of cytochrome b is fairly conserved
over a large number of species (fig. 19.9)
Molecular Comparisons
 In amino acid sequences, single substitutions
may have large or small effects based on the
amino acid that is replaced and what it is
replaced with
 Most mutations that affect phenotype are
selected against, some may prove adaptive
 Similarities in proteins do not always equal
similarity in DNA sequence because of the
redundancy in the genetic code
Molecular Comparisons
 Mitochondrial DNA can also be sequencing
analysis
 Mitochondria can be used to determine
familiar relationships because the
mitochondrial DNA is passed on intact
without the effects of crossing over during
meiosis or recombination during fertilization
Making Data Into Trees
CHAPTER 19.5
Making Data into Trees
 In order to elucidate evolutionary
relationships evolutionary biologists use
genomic analysis, morphological analysis, or
biochemical analysis (or even combinations
of the 3) to describe the character differences
Making Data into Trees
 Parsimony analysis: done to determine he
most logical connections between species
 Parsimony and the basic rule of cladistics, is
that simplicity guides relationships
 The closer a relationship between species, the
least amount of differences
 Evolutionary trees with fewest differences are
more likely to be correct
Preview of Life’s Evolutionary History
CHAPTER 19.6
Preview of Life’s
Evolutionary History
 Hawaiian Honeycreepers:
 A period of adaptive
radiation led to a series of
new Honeycreeper species
emerging
 However, now that many of
these species are becoming
extinct due to predation and
competition, their genetic
diversity is declining
Preview of Life’s
Evolutionary History
 Phylogeny is an ongoing field of research
 We are constantly refining our understanding
of evolutionary relationships
Preview of Life’s
Evolutionary History
 Several ways of defining he big picture of
evolution exist
 Some evolutionary biologist use a 6 kingdom
model where prokaryotes fit into either the
bacteria or Archea Kingdom while Plants, Animals,
Protists, and Fungi each have their kingdom
 Other evolutionary biologists use a 3 domain
system where Archea, Bacteria, and Eukaryotes
have their own domain