The document summarizes key concepts about phylogenetic classification and evolutionary relationships. It describes Linnaeus's original classification system based on observable characteristics rather than evolutionary relationships. After Darwin, phylogeny emerged as the study of evolutionary history and relationships among organisms. Phylogenetic trees graphically represent evolutionary histories and show ancestor-descendant relationships. They are constructed based on identifying shared derived characteristics. The relationships depicted can differ depending on whether trees are based on morphological or molecular data.

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2.  Linnean Classification System; 2 main characteristics:
*Binomial nomenclature …Each organism has a 2 part name
consisting of genus and species
*Hierarchical classification scheme

3.  Groups species into increasingly broad categories… For
example, species that appear to be closely related are
grouped into the same genus

4.  However… Linneaus’s classification was not based on
evolutionary relationships but simply on resemblances
between organisms.; what characteristics they had in
common
 After Darwin, scientists began classifying organisms
based on phylogeny
Phylogeny=the study of the evolutionary history or
relationships among organisms

5.  Problems can arise because similar traits can evolve
independently in two distant species rather than from in
a common ancestor.
 Homology occurs when traits are similar due to shared
ancestry.
 Homoplasy (aka: analogy) occurs when traits are
similar for reasons other than common ancestry
 Convergent evolution… when natural selection favors
similar solutions to problems posed by a similar way of
life… structures in unrelated organisms evolve to perform
similar function

6.  Phylogenies are usually summarized and depicted in
the form of a phylogenetic tree… graphical
representation of evolutionary history
 shows ancestor-descendant relationships among
groups of organisms
*In this lab today, you will learn how to construct,
read, and interpret a phylogenetic tree

7.  A branch represents a population through time
 A node (or fork), the point where two branches
diverge… represents the point in time when an
ancestral group split into two or more descendant
groups
 The root is the first or most basal node on the tree
 A tip (or terminal node), the endpoint of a
branch, represents a group (a species or larger taxon)
that is living today or ended in extinction.

8. *Left is the most ancient. As move to the right (or up the tree) become
more recent
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9. Outgroup… Species or group of species that is closely
related to, but not a member of, the group under study
(ingroup)
 Serves as a basis of comparison
 Assumed to represent a distant ancestor
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10.  There are many equivalent ways of drawing the same tree

11.  The cladistic approach to inferring trees is based on
identifying the shared derived characteristics of the
group under study… synapomorphies
 Synapomorphy is a trait that certain groups of
organisms have that exists in no others
 Synapomorphies are characteristics that are shared
because their common ancestor had them

12.  Allow biologists to recognize monophyletic groups—
also called clades or lineages.
 Clade
 Species that share a common ancestor as
indicated by the possession of shared derived
characters
 Evolutionary units; refer to a common ancestor
and all descendants
 Cladogram= type of phylogenetic tree
*This is the approach we will be using!!!

13.  An ancestral trait is a characteristic that existed in an
ancestor; prior to the common ancestor of the group
 A derived trait is one that is a modified form of the ancestral
trait, found in a descendant; similarity that is inherited from
the most recent common ancestor of an entire group
 Ancestral and derived traits are relative.

14.  Characters should exist in recognizable character states
 Present or Absent
 Example: Character “hair” in vertebrates has two
states…present in mammals and absent in fish,
amphibians, and reptiles
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15. “1” = ; the organism has the trait; possession of derived character state
“0” = the organism lacks the trait; possession of ancestral character state

16. The derived characters between the cladogram branch points are
shared by all organisms above the branch points and are not present in
any below them. The outgroup (in this case, the lamprey) does not
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possess any of the derived characters.

17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Salamander Frog Lizard Tiger Gorilla Human Salamander Lizard T iger Frog Gorilla Human
Hair loss
Amniotic
membrane
loss
Hair Tail loss
Amniotic Hair
membrane Amniotic
Tail loss membrane
a. b.
Based on the principle of parsimony, the cladogram that
requires the fewest number of evolutionary changes is
favored
Parsimony…principle of logic stating that the most likely
explanation is the one that implies the least amount of
change.; It favors simple explanations over complicated ones
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18. *What type of data to scientists look at when trying to
reconstruct phylogenies?
 Morphology (e.g. stuctures)*
 Molecular (e.g. DNA sequences)*
 Physiology
 Behavior
*When use morphological characteristics vs. molecular characteristics can
get very different results… different possible evolutionary relationships

19. *Phylogeny Activities…
Activity 1: Constructing a simple phylogenetic tree
Activity 2: Reading and interpreting a phylogenetic
tree… compare a tree based on morphological data and
a tree based on molecular data
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20. STEP 1: Choose a group of organisms
STEP 2: Choose the traits (or characters) you will compare
in your clade
STEP 3: Polarize the characters… this means to determine
presence or absence; You then have to determine if the
characters are ancestral or derived
STEP 4: Group the organisms by shared derived characters
STEP 5: Using those groupings, create a cladogram
Shared derived traits are listed after branch points
Organisms go at the tips of the branches
20 *Steps 1 and 2 all already done for you

21.  Artiodactyls, including hippos, cows, deer, and
pigs, are mammals that have hooves, an even number
of toes, and an unusual pulley-shaped ankle bone
(astragalus).
 Traditionally, phylogenetic trees based on
morphological data place whales as the outgroup
 DNA sequence data, however, suggest a close
relationship between whales and hippos. This tree
would require two changes to the astragalus trait.

22.  Recent data on gene sequences called short interspersed nuclear
elements (SINEs) show that whales and hippos share several SINE
genes that are absent in other artiodactyl groups.
 These SINEs are shared derived traits (synapomorphies) and support
the hypothesis that whales and hippos are indeed closely related.

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24.  Development proceeds in ordered phases
 Gametogenesis... Formation of sperm and egg
 Fertilization… sperm and egg unite to form a zygote
(fertilized egg)
 Cleavage… zygote undergoes cell division
 Gastrulation
 Organogenesis
*Sexual Reproduction

25.  Cleavage is the set of rapid cell divisions that take place
in a zygote immediately after fertilization… mitosis!
 Cleavage is the first step in the process that makes a
single-celled zygote into a multicellular embryo
 The cells created by cleavage divisions are called
blastomeres… have specific fates
 Eventually you get a ball of cells called a morula

26.  When cleavage is complete the embryo consists of a
hollow ball of cells called a blastula
 Blastocoel – fluid-filled cavity

27.  Cleavage partitions the egg cytoplasm without any
additional growth taking place… No increase in the
overall size of the embryo
 Rapid division of the zygote into a larger and larger
number of smaller and smaller cells (blastomeres)
 Animal pole
 Forms external tissues
 Vegetal pole
 Forms internal tissues
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28.  Cleavage patterns are quite diverse
 Relative amount and distribution of nutritive yolk in the
egg is the characteristic that most affects the cleavage
pattern of an animal embryo
Sea Urchin Frog Chicken
Animal pole
Cytoplasm Cytoplasm Nucleus Shell
Nucleus
Plasma
Nucleus Air membrane
bubble Albumen
Yolk
Yolk
Vegetal pole Yolk
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a. b. c.

29.  Eggs with little or no yolk (or
moderate yolk)
 Holoblastic (complete)
*
cleavage
 Invertebrates, amphibians,
*
mammals
 Eggs with large amounts of yolk
 Meroblastic (incomplete)
cleavage
 Fish, reptiles, birds
 Embryo forms thin cap on yolk
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30.  Gastrulation begins with the formation of the
blastopore…blastula indents to form a gastrula with a
blastopore = opening to outside
 Cells from the periphery move inward through the
blastopore, forming a tube-like structure that will become
the gut… archenteron = Primitive gut

31.  During gastrulation, extensive and highly organized
cell movements radically rearrange the embryonic cells
into a structure called the gastrula
 Gastrulation results in the formation of embryonic
tissue layers.
 Most early embryos have 3 primary tissue layers:
ectoderm, mesoderm, and endoderm
 These embryonic tissues are called germ layers
because they give rise to adult tissues and organs.

32.  Ectoderm forms the outer
covering of the adult body
and the nervous system.
 Mesoderm gives rise to
muscle, most internal
organs, and connective
tissues such as bone and
cartilage.
 Endoderm produces the
lining of the digestive tract
or gut, along with some of
the associated organs.

33.  At the end of gastrulation, the three embryonic
tissues are arranged in layers, the gut has formed, and
the major body axes have become visible.

34.  Organogenesis is the process of tissue and organ
formation that begins once gastrulation is complete
and the embryonic germ layers are in place.
 During organogenesis, cells proliferate and become
differentiated, meaning that they become a
specialized cell type.

35. http://www.youtube.com/watch?v=lXN_sDnd1ng
http://www.youtube.com/watch?v=2V2_aTiOwj4&feature
=topics
http://www.youtube.com/watch?v=Lgb4wMsZwZA&featu
re=topics
http://www.youtube.com/watch?v=qisrNX3QjUg&feature
=related

36.  Based on certain aspects of early development, most
animals are categorized as having one of two
developmental patterns
 Protostome development… “first mouth”
*Arthopods, Mollusks, Annelids
 Deuterostome development… “second mouth”
*Echinoderms and Chordates

37. Protostomes and Deuterostome differ from each other in 4
fundamental embryological features:
1. Cleavage pattern of embryonic cells
2. Developmental fate of cells
3. Fate of the blastopore
4. Origin of the coelom*
*will discuss this at later date
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38. Protostomes… spiral cleavage
*the first two divisions are equal, but the rest are unequal.
*planes of cell division are diagonal to the vertical axis of the
embryo; upper cells lay in the grooves between the underlying
cells
Deuterostomes… radial cleavage
*each cell division is equal and results in cells of all the same size
*planes of division are either parallel or perpendicular to the
vertical axis of the embryo; tiers of cells are aligned, one directly
above the other

39. *Difference between spiral & radial can be seen at 8-cell stage
http://worms.zoology.wisc.edu/urchins/rad_spir.html

40. Protostomes… determinate (mosaic) development
*developmental fate of each embryonic cell is determined
very early
Deuterostomes… indeterminate (regulative) development
*each cell produced by early cleavage divisions retains the
capacity to develop into a complete embryo

41. Protostomes… develop the mouth first from or near the
blastopore
Deuterostomes… develop the anus first from the
blastopore
41

42. *You are going to compare
spiral cleavage in a ribbon
worm (a protostome) with
radial cleavage in a sea star
(a deuterostome)
42

43. *Spiral Cleavage: The Ribbon Worm, Cerebratulus
unfert egg fert egg (zygote) 2 cell 4 cell
8 cell morula blastula gastrula
later gastrula later in dev

44. *Radial Cleavage: The Sea Star, Asterias
unfert egg fert egg
early cleavage
late cleavage blastula
gastrula
http://www1.broward.edu/~fsearcy/Zoology/index.htm