Chapter 16:
Key Terms:
Ancestral trait: precursor to derived trait; less complex trait found in a variety of living
organisms
Binomial nomenclature: composed of the genus and species (sometimes subspecies too) of
an organism to identify it; two words (first is capitalized, both italicized); latin
Clade: taxa with the same common ancestor
Convergent evolution: when similar traits are derived from nonrelated groups
Derived trait: evolved from an ancestral trait
Evolutionary reversal: when a trait reverts back to the ancestral trait
Genus: first name in binomial nomenclature
Homologous: traits shared by 2+ species inherited from a common ancestor
Homoplasies or homoplastic trait: results of convergent evolution
Ingroup: organism(s) of interest
Lineage: sequence of species that form a line of descent where each new species is the
direct result of speciation from an immediate ancestral species
Maximum likelihood: examines data in terms of probability that it would give rise to the
supported data set; greater probability is better that lesser
Molecular clock: uses fossils and rates of molecular change to determine the divergence of
a species
Monophyletic: organisms share a single common ancestor; clade
Outgroup: organism that shares the least in common with the ingroup
Paraphyletic: groups with organisms missing
Parsimony Principle: state things in simplest explaination or representation possible;
assume traits evolved only once
Phylogenetic tree: depiction of phylogeny; roots are common ancestor or gene, nodes are
when 2 species or genes split; speciation occurs from right to left along a timeline
Phylogeny: grouping individuals with a similar lineage
Polyphyletic: groups with organisms with multiple common ancestors
Sister clade: similar clades
Sister species: closest relatives to a species
Species: second name in binomial nomenclature
Synapomorphies: shared, derived traits
Systematics: study of diversification of life and relationships among species through time
Taxon: “end branch on a phylogenetic tree;” species
(Most Inclusive)
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Subspecies
(Most
Exclusive)
Questions:
1. Synapomorphies are shared, derived traits and they are the result of speciation.
Two species share most of the same traits, but in some way they are different
enough to be two separate species. The traits in common are synapomorphies.
2. A phylogenetic tree shows relationships among species and who their ancestors are.
3. A clade is a group of taxa with the same common ancestor. Sister species are part of
the same clade and sister clades are clades that have similar traits/ancestors but
have less in common that the sister species.
4. Clades are based on certain traits that organisms have in common. They are based
on DNA and computer models so they are more accurate. The old classification
method is based on morphology and is less accurate because homoplastic traits
mess up the data.
5. See #4
6. Convergent evolution is when similar traits are derived from nonrelated groups, like
bird and bat wings.
7. Environmental conditions that selected for an ancestral trait could cause an
evolutionary reversal.
8. Homology is two traits with the same origin (divergent evolution), while homoplasy
is two traits with nonrelated origins (convergent evolution).
9. The bat and bird wings are homoplastic, but the bones that make up the wings are
homologous.
10. The outgroup has the least in common with the other organisms of interest, or the
ingroup.
11. The parsimony principle requires that things are stated in simplest explanation or
representation possible and assume traits evolved only once. If traits evolved only
once then they will only be on the phylogenetic tree at one node. If they “evolve” at
more that one node on the tree, then the parsimony principle is not being followed.
12. DNA data is organized by computers and then laid out in a phylogenetic tree to be
analyzed by geneticists. In the past, only morphology was used to determine the
relationships of species, but now scientists analyze morphology in addition to DNA,
behavior, development, and molecular data.
13. Scientists today can study a phylogenetic tree to trace the descent of a certain gene.
If an epidemiologist is tracing the evolutionary path of the HIV virus, they can
analyze where it entered the human population and how it has evolved since then. If
certain medicines worked when the virus had certain proteins, then hopefully the
scientists can see what proteins the current HIV has and make medication for that.
14. See above for monophyletic, paraphyletic, polyphyletic definitions. Monophyletic is
best because it means that one organism has one common ancestor with another
species. The data is clear and there are no ambiguities as to the descent of that
organism.
Questions about Phylogeny Practice (Chart Built Below):
1. Pine Tree and Sunflower are most closely related.
2. Pine Tree and Sunflower are sister species because they have seeds in common.
3. Vascular Cells and True Roots evolved along the same branch.
4. After the trait names were rearranged, there were no homoplasies.
Pine Tree
Seeds
Megaphylls
(True
Leaves)
Vascular
Cells/Tru
e Roots
Persistently
Green
Sporophyte
Sunflower
Bracken Fern
Club Moss
Stomata
Protected
Embryos
Hornwort
Common
Ancestor
Sphagnum Moss
Liverwort
Stonewart