AP Biology Chapter 26
Phylogeny and the Tree of Life
Objectives
The Fossil Record and Geologic Time
1. Distinguish between phylogeny and systematic.
-Phylogeny is the evolutionary history of a species or group. Systematics is the
discipline focused on classifying organisms and determining evolutionary
relationships.
2. Describe the process of sedimentation and the formation of fossils. Explain what portions
of organisms mostly fossilize and why.
-In fossil formation, an animal or plant must die in water or near enough to fall
into shortly after death. The water insulates the remains from many of the
elements that contribute to decomposition. The portion that becomes fossilize is
mostly the exoskeleton because bacteria would consume the soft body parts. In
sedimentation, sediments bury the exoskeleton as time passes. The faster this
happens, the more likely the fossilization. (land or mud slides help)
3. Distinguish between relative dating and absolute dating.
-Relative dating determines the order in which a series of events occurred of an
artifact or paleontological site, whereas absolute dating is the process of
determining a specific date for an archaeological or paleontological site or
artifact.
4. Explain how isotopes can be used in absolute dating.
-Radioactive isotopes have a fixed rate of decay, which can be used in absolute
dating. For example, carbon-14 has a half life of 5,730 years, so, isotopes that
decay more slowly can be used to infer the age of fossils associated with the
layers of rock. Radioactive isotopes only decay in fixed rate after organism dies.
5. Explain why the fossil record is incomplete.
-Very few organisms were preserved as fossils, organisms tend to decay before
becoming fossilized, only organisms with exoskeletons could be preserved, and
some organisms left over’s may be destroyed in the process.
6. Describe two dramatic chapters in the history of continental drift. Explain how those
movements affected biological evolution.
-One dramatic continental drift was in the southern tip of Labrador, Canada where
it has moved 40 degree north over the last 200million years. Another was in
Wilmington, Delaware, where the shift had caused the weather to drop
dramatically. In affect to biological evolution, it has caused temperature shifts,
and geographical shifts. It also causes geographical isolation.
7. Explain how mass extinctions have occurred and how they affected the evolution of
surviving forms.
-Mass extinction have occurred due to the organism’s habitat being destroyed,
its environment may have been changed in a manner unfavorable to the species,
and or any other disruptive global environmental changes. When a dominant
specie becomes extinct, its ecological niches passes to another specie.
8. Describe the evidence related to the impact hypothesis associated with the Cretaceous
extinctions. Describe the hypothesized consequences of such an impact.
-The hypothesis was that the cretaceous mass extinction marks the boundary
between the Mesozoic and Cenozoic eras about 65.5 mya, claimed more than
one-half of the marine species, many families of terrestrial plants and animals,
and most dinosaurs. The affect is that a thin layer of clay rich iridium may have
been released from a cloud of dust, which may block sunlight, affecting weather.
Systematics: Connecting Classification to Phylogeny
9. Distinguish between systematics and taxonomy.
-Systematics is the discipline focused on classifying organisms and determining
evolutionary relationships. Taxonomy is concerned with naming and classifying
species.
10. Explain how species are named and categorized into a hierarchy of groups.
-Charles Linnaeus made an approach for the species’ names. The first part was
called a genus (in Latin, plural, genera), to which the species belong. The second
part is called the specific epithet, which is unique for each species within the
genus. These organisms are grouped in binomial
11. List the major taxonomic categories from the most to least inclusive.
-The first grouping is built into the binomial: Species that appear to be closely
related are grouped into the same genus. The taxonomic system named after
Linnaeus, called the Linnaean system, places related genera into the same family,
families into orders, orders into classes, classes into phyla, phyla into kingdoms,
and recently, kingdoms into domains.
12. Define the parts and describe the interrelationships within a cladogram. Explain how a
cladogram is constructed.
-In this methodology, biologists place species into groups called clades, each of
which includes an ancestral species and all of its descendents. Clades are nested
within larger clades. Cladograms are constructed by comparing organisms to see
if they share a trait or derived character, and are then constructed as a series of
Y’s or branches. At every branch, one of the organisms that do not share a
common character with the rest of the group is “branched off” into its own clade.
13. Distinguish between homologous and analogous structures. Explain why the similarity of
complex systems implies a more recent common ancestor.
-homologous structures are structures in different species that are similar because
of common ancestry, whereas analogous structures are structures that have
similar functions but have not evolved from a common ancestry. The higher the
resemblance of two complex systems, the more that it implies common ancestor.
14. Distinguish between shared primitive characters and shared derived characters. Compare
the definitions of an ingroup and outgroup.
-shared primitive (ancestral) character, is a character shared by members of a
particular clade, that originated in an ancestor that is not a member of that clade.
Shared derived character is an evolutionary novelty that is unique to a particular
clade. An outgroup is a species or group of species from an evolutionary lineage
that is known to have diverged before the lineage that includes the species that
we are studying, or an ingroup.
15. Compare the cladistic and phylocode classification systems.
-Cladistics is an approach to systematic in which organisms are placed into groups
called clades based primarily on common descent, and phylocode is a system of
classification of organisms based on evolutionary relationships, in which only
groups that include a common ancestor and all of its descendants are named.
16. Explain how nucleotide sequences and amino acid sequences can be used to help classify
organisms. Explain the advantage that molecular methods have over other forms of
classification.
-With molecular comparison, scientists can study the nucleotide sequences of
organisms. They created a program to take into account insertions, deletions, and
substitutions. They found that the many differences between the two in
in comparison revealed a great amount of divergence therefore they’re not
closely related or common in ancestry.
17. Explain the principle of parsimony. Explain why any phylogenetic diagram is viewed as a
hypothesis.
-The principle of parsimony favors the hypothesis that requires the fewest or
simplest assumptions to explain an observation. Any phylogenetic diagram is
viewed as a hypothesis because there is no way to measure whether a particular
phylogenetic hypothesis is accurate or not, and the diagram requires a lot of
assumptions and approximations as well.
18. Explain how molecular clocks are used to determine the approximate time of key
evolutionary events. Explain how molecular clocks are calibrated in the actual time.
-A molecular clock is basically a yardstick for measuring the absolute time of
evolutionary change based on the observation that some genes and other regions
of genomes appear to evolve at a constant rate. We can calibrate the molecular
clock of a gene that has a reliable average by graphing the number of genetic
differences against the dates of evolutionary branch points that are known from
the fossil record.
19. Explain how scientists determined the approximate time when HIV first infected humans.
-By comparing sequences of HIV viruses from samples taken at various times
during the epidemic, researchers have observed a remarkably consistent rate of
evolution. They estimate that the HIV-1 M strain first infected humans in the
1930s.
20. Describe an example of a conflict between molecular data and other evidence, such as the
fossil record. Explain how these differences can be addressed.
-The problem is that there is no definite and exact approach in solving or exactly
dating the time period. These methods each have a different approach and are
quite accurate, but it is not exact.
Vocabulary
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Phylogeny: The evolutionary history of a species or group of related species.
Fossil record: Fossils that are the preserved remains or traces of animals, plants, and other
organisms from the remote past.
Geologic time scale: The geologic time scale provides a system of chronologic
measurement relating stratigraphy to time that is used by geologists, paleontologists, and
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other earth scientists to describe the timing and relationships between events that have
occurred during the history of the earth.
Radiometric dating: A method for determining the absolute ages of rocks and fossils,
based on half life of radioactive isotopes.
Half life: The amount of time it takes for 50% of a sample of radioactive isotope to
decay.
Pangaea: The supercontinent that formed near the end of the Paleozoic era, when plate
movements brought all the landmasses of earth together.
Systematics: A scientific discipline focused on classifying organisms and determining
their evolutionary relationships.
Binomial: The two-part Latinized name of a species, consisting of the genus and specific
epithet.
Genus: A taxonomic category above the species level, designated by the first word of a
species’ two-part scientific name.
Specific epithet: The second element in the Latin binomial name of a species, which
follows the generic name and distinguishes the species from others in the same genus.
Species: A population or group of populations whose members have the potential to
interbreed in nature and produce viable, fertile offspring, but do not produce viable,
fertile offspring with members of other such groups.
Family: In classification, the taxonomic category above genus.
Order: In classification, the taxonomic category above the level of family.
Class: In classification, the taxonomic category above the level of order.
Phyla (singular, phylum): In classification, the taxonomic category above class.
Kingdoms: A taxonomic category, the second broadest after domain.
Domain: A taxonomic category above the kingdom level. The three domains are archaea,
bacteria, and eukarya.
Taxon (plural, taxa): A named taxonomic unit at any given level of classification.
Phylogenetic tree: A branching diagram that represents a hypothesis about the
evolutionary history of a group of organisms.
Cladogram: A branching diagram showing the cladistic relationship between a number of
species.
Clade: A group of species that includes an ancestral species and all its descendents.
Monophyletic: Pertaining to a group of taxa that consists of a common ancestor and all its
descendents. A monophyletic taxon is equivalent to a clade.
Homology: Similarity in characteristics resulting from a shared ancestry.
Convergent evolution: The evolution of similar features in independent evolutionary
lineages.
Analogy: Similarity between two species that is due to convergent evolution rather than
to descendent from a common ancestor with the same trait.
Shared primitive character: A character, shared by members of a particular clade, that
originated in an ancestor that is not a member of that clade.
Shared derived character: An evolutionary novelty that is unique to a particular clade.
Outgroup: A species or group of species from an evolutionary lineage that is known to
have diverged before the lineage that contains the group of species being studied. An
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outgroup is selected so that its members are closely related to the group of species being
studied, but not as closely related as any study-group members are to each other.
Ingroup: A species or group of species whose evolutionary relationships we seek to
determine.
Phylocode: System of classification or organisms based on evolutionary relationships:
Only groups that include a common ancestor and all of its descendents are named.
Parsimony: A principle that states that when considering multiple explanations for an
observation, one should first investigate the simplest explanation that is consistent with
the facts.
Molecular clocks: A method for estimating the time required for a given amount of
evolutionary change, based on the observation that some regions of genomes appear to
evolve at constant rates.
Phylogenetic fuse: a combination of phylogenics.