The Tree of Life: Phylogenetic Reconstruction

Question 1

Describe how evolution can be depicted as a tree with nested relationships among phylogenies, species, opulations, lineages, and individuals.

Answer 1

e can think of the succession of generations in a population as the growing tip of a branch. A population may become subdivided into two populations that no longer exchange genes, making it possible for them to diverge into two separate species. Evolutionary biologists represent this splitting as a single branch dividing into two or more new branches. Those new branches can, in time, split into new ones as well. Depicting the evolution of a lineage into branches is known as a phylogeny.

Question 2

What is a monophyletic group?

Answer 2

Monophyletic describes a group of organisms that form a clade. A clade is a single “branch” in the tree of life; each clade represents an organism and all of its descendants.

Question 3

What is a paraphyletic group?

Answer 3

Paraphyletic describes a group of organisms that share a common ancestor, although the group does not include all the descendants of that common ancestor.

Question 4

What is a polyphyletic group?

Answer 4

Polyphyletic describes a taxonomic group that does not share an immediate common ancestor and therefore does not form a clade.

Question 5

Explain how synapomorphic character states are used to reconstruct a phylogeny.

Answer 5

Phylogenies are reconstructed using shared derived characters (aka synapomorphies) to identify
clades (monophyletic groups).
Homologies help us reconstruct phylogenies because we can group lineages together based on homologous traits. All synapomorphies appear on the tree only once unless the character state was derived separately by evolutionary parallelism/ convergent evolution.

Question 6

Compare and contrast the following terms: synapomorphy, homoplasy, convergent evolution, and evolutionary reversal.

Answer 6

Synampomorphy, homoplasy, convergent evolution, and evolutionary reversal all have to do with the characteristics of organisms. Synapomorphy and homoplasy refer to the origin of the characteristic. Synapomorphies imply a homologous trait is the product of common ancestry, while homoplasies a similar characteristic that is not due to common descent. Convergent evolution and evolutionary reversal are both mechanisms by which homoplasies occurr. Convergent evolution is the development of similar characteristics due to similar selective pressures from similar environments or bioms, while evolutionary reversal is the reversion back to an ancestral character state though, for example, a mutation.

Question 7

Which statement about a node of a phylogenetic tree is
correct?
A. A node connects two speciation events.
B. A node represents the point at which a lineage splits.
C. A node refers to the common ancestor of all the taxa
shown in the tree.
D. A node depicts currently living species.

Answer 7

B. A node represents the point at which a lineage splits.

Question 8

A clade
A. is a visual representation of the evolutionary history of
populations, genes, or species.
B. represents an ancestor and all its descendants.
C. represents a speciation event.
D. describes a grouping of taxa that does not include the
common ancestor of all the members of the taxon.

Answer 8

B. Represents an ancestor and all its descendants.

Question 9

Which statement about the root of a phylogenetic tree is
correct?
A. A rooted tree shows which node is the common
ancestor of all the taxa shown in the tree.
B. A rooted tree does not contain information about
which character states are ancestral and derived.
C. In a rooted tree, the root is indistinguishable from the
tips of the tree.
D. An unrooted tree cannot be used to depict
evolutionary relationships among plants.

Answer 9

A. A rooted tree shows which node is the common ancestor of all the taxa shown in the tree.

Question 10

What is the main difference between a paraphyletic group
and a polyphyletic group?
A. There are no differences because they both describe
the same grouping pattern in phylogenetic trees.
B. A polyphyletic group does not include all the
descendants of a common ancestor, whereas
paraphyletic groups do not share an immediate
common ancestor.
C. A paraphyletic group does not include all the
descendants of a common ancestor, whereas
polyphyletic groups do not share a most recent common
ancestor.
D. Paraphyletic groups form clades.

Answer 10

C. A paraphyletic group does not include all the
descendants of a common ancestor, whereas
polyphyletic groups do not share a most recent common
ancestor.

Question 11

Homoplasy

Answer 11

Character state similarity not due to common descent.