Classification and Phylogeny - Directed Reading
Name: ANSWER KEY
As you read from page 492 – 501, answer the following questions.
1.
What is systematics?
The study of biological diversity in an evolution context. Tracing phylogeny is one of the main goals of
systematics.
2. Taxonomists use a binomial name to each organism. What two parts make up the binomial name? Give an
example of a binomial name. What is the purpose of a binomial name (ie – why do we use them?)
Two parts: Genus and species
Example: Homo sapiens, E. coli, Panthera pardus
Purpose: We use scientific names because they are based upon classification and they give us a common
language to use within the scientific community.
3. Starting with Domain, write out the eight levels of classification.
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
4. Using the diagram to the right, fill in the eight taxons and the
name of each taxon the leopard (Panthera pardus) belongs to.
5. What is a phylogenetic tree?
A grouping of organsisms that reflect the heirarchaical
classification of taxonomic groups nested within more inclusive
groups.
6. What is a cladogram?
A tree constructed from a series of dichotomies, or two-way
branch points. Each of the branch points represents the
divergence of two species from a common ancestor.
7. To the right is a sample of a cladogram with a leopard and a domestic cat.
What does the branch between them represent? What does the “deeper”
branch point represent? (ie – what would we place at the bottom of the y?)
The branch represents the divergence of the two species from a common
ancestor. The deeper branch point represents the common ancestor.
8. What do each of the following groupings on the cladogram represent?
Monophyletic – A clade containing an ancestral species and all of its decendants.
Paraphyletic – An ancestor and some of its descendants.
Polyphyletic – A taxon that does not contain a common ancestor.
9. Define
a. homology – a likeness due to a shared ancestry, EX: forelimbs of mammals
b. analogy – a likeness due to convergent evolution EX: wings on bats and birds
10. How can we determine the difference between homology and analogy?
The greater the number of homologous parts, the more closely the species are related.
The more complex two structure are, the less likely they evolved independently EX: the skull of a
chimpanzee and a human
11. Scientists must also determine if a characteristic is a shared primitive characteristic or a shared derived
characterisitic. For example, lets look at the presence of a backbone. We can not use just the presence of
a backbone to identify and distinguish mammals since fish and reptile also have backbones. Therefore, the
backbone is a homology that came before the branching of the mammalian clade from the vertebrate tree
and is a shared primitive characteristic. It is common to a taxon that is more inclusive (larger) than the
one we are looking at. In contrast, hair is a homology found only in the vertebrates called mammals. If we
compare mammals to other vertebrates, hair is a shared derived characteristic. This tells us it is an
evolutionary novelty unique to a particular clade. Fill in the flow chart below that summarizes our findings.
Analogies
All
similar
characters
Primitive
(ancestral)
Homologies
Derived
(unique to a
clade)
12. In order to construct a cladogram, scientists will compare the organism they are relating with an outgroup.
What is an outgroup and why is it used?
An outgroup is a species or group of species that is closely related to the species being studies, but is
known to be less closely related than any of the study-group members are to each other. This is based on
evidence from paleontology, embryonic development, and molecular biology.
13. Using the example given on page 497, fill in the character table and cladogram given below.
14. What does a cladogram represent?
A cladogram represents the chronological sequence of branching during the evolutionary history of a set of
organisms.
15. True of False: The turtle in question 13 has evolved more recently than the salamander. If you choose
false correct this statement.
FALSE: It means that the common ancestor of the salamander preceded the ancestor of the turtle-leopard
clade. Chronology in a cladogram is relative rather than absolute.
16. Cladograms can be used to place species in the taxonomic hierarchy of groups within groups. Using the diagram
to the right, label the nested circles with the taxa they represent.
House cat and Leopard: Family
Wolf, Leopard, and House cat: Order
Horse, Wolf, Leopard, and House cat: Class
17. Up to this point, we’ve based out cladograms on physical characteristics. What other piece of evidence
could be used to construct a cladogram?
DNA sequences
18. What does the principle of parsimony tell us?
A theory about nature should be the simplest explanation that is consistent with the facts. IE – “keep it
simple”. Parsimony is sometimes called Occam’s Razor.
19. Use the data and charts on pages 500 – 501. Based on the three hypothesized cladograms of bird species
below, which is the best representation of evolutionary relationships between the species? Why do we
come to this conclusion?
Based upon the data give in the textbook, The first (or left)
cladogram drawn above is the most correct. When using the DNA
sequence data in the table to the left, it becomes clear after some
analysis that the least number of evolutionary events would occur
with the first hypothesized cladogram. Keeping with parsimony, the
least number of evolutionary events is the most simplest explanation
and therefore, most likely the best answer.