Phylogeny and the Tree of Life

VISUAL SKILLS- Which levels of the classification in Figure 26.3 do humans share with leopards?

Which of the trees shown here depicts an evolutionary history different from the other two? Explain.

The bear family (Ursidae) is more closely related to the badger/otter family (Mustelidae) than to the dog family (Canidae). Use this information to redraw Figure 26.4.

Suppose that two species, A and B, have similar appearances but very divergent gene sequences, while species B and C have very different appearances but similar gene sequences. Which pair of species is more likely to be closely related: A and B or B and C? Explain.

Suppose that two species, A and B, have similar appearances but very divergent gene sequences, while species B and C have very different appearances but similar gene sequences. Which pair of species is more likely to be closely related: A and B or B and C? Explain.

To distinguish a particular clade of mammals within the larger clade that corresponds to class Mammalia, would hair be a useful character? Why or why not?

The most parsimonious tree of evolutionary relationships can be inaccurate. How can this occur?

Draw a phylogenetic tree that includes the relationships from Figure 25.7 and Figure 26.16. Traditionally, all the taxa shown besides birds and mammals were classified as reptiles. Would the cladistic approach support that classification? Explain.

Explain how comparing proteins of two species can yield data about the species’ evolutionary relationship.

WHAT IF? Suppose gene A is orthologous in species 1 and species 2, and gene B is paralogous to gene A in species 1. Suggest a sequence of two evolutionary events that could result in the following: Gene A differs considerably between species, yet gene A and gene B show little divergence from each other.

MAKE CONNECTIONS Review Figure 18.13, then suggest how a particular gene could have different functions in different tissues within an organism.

What is a molecular clock? What assumption underlies the use of a molecular clock?

Review Concept 17.5. Then explain how numerous base changes could occur in an organism’s DNA yet have no effect on its fitness.

Suppose a molecular clock dates the divergence of two taxa at 80 million years ago, but new fossil evidence shows that the taxa diverged at least 120 million years ago. Explain how this could happen.

In the rows of data for the organisms being compared with theaphid, highlight the amino acids that are identical to the corresponding amino acids in the aphid.

Which organism has the most amino acids in common with the aphid? Rank the partial polypeptides from the other four organisms in degree of similarity to that of the aphid.

Do these data support the hypothesis that aphids acquired the gene for this polypeptide by horizontal gene transfer? Why or why not? If horizontal gene transfer did occur, what type of organism is likely to have been the source?

What additional sequence data would support your hypothesis?

How would you account for the similarities between the aphid sequence and the sequences for the bacteria and plant?

Why is the kingdom Monera no longer considered a valid taxon?

Explain why phylogenies based on different genes can yield different branching patterns for the tree of all life.

Explain how the origin of eukaryotes is thought to have represented a fusion of organisms, leading to extensive horizontal gene transfer. (See Figure 25.10.)

In a comparison of birds and mammals, the condition of having four limbs is

(A) a shared ancestral character.

(B) a shared derived character.

(C) a character useful for distinguishing birds from mammals.

(D) an example of analogy rather than homology.

To apply Parsimony to constructing a phylogenetic tree,

(A) choose the tree that assumes all evolutionary changes are equally probable.

(B) choose the tree in which the branch points are based on as many shared derived characters as possible.

(C) choose the tree that represents the fewest evolutionary changes, in either DNA sequences or morphology.

(D) choose the tree with the fewest branch points.

VISUAL SKILLS In Figure 26.4, which similarly inclusive taxon

is represented as descending from the same common ancestor

as Canidae?

(A) Felidae

(B) Mustelidae

(C) Carnivora

(D) Lutra

Three living species X, Y, and Z share a common ancestor, T, as

do extinct species U and V. A grouping that consists of species

T, X, Y, and Z (but not U or V) makes up

(A) a monophyletic taxon.

(B) an ingroup, with species U as the outgroup.

(C) a paraphyletic group.

(D) a polyphyletic group.

VISUAL SKILLS Based on the tree below, which statement is

not correct?

(A) Goats and humans form a sister group.

(B) Salamanders are a sister group to the group containing

lizards, goats, and humans.

(C) Salamanders are as closely related to goats as to humans.

(D) Lizards are more closely related to salamanders than to

humans.

If you were using cladistics to build a phylogenetic tree of cats,

which of the following would be the best outgroup?

(A) wolf

(B) domestic cat

(C) lion

(D) leopard

VISUAL SKILLS The relative lengths of the frog and mouse

branches in the phylogenetic tree in Figure 26.13 indicate that

(A) frogs evolved before mice.

(B) mice evolved before frogs.

(C) the homolog has evolved more rapidly in mice.

(D) the homolog has evolved more slowly in mice.

Darwin suggested looking at a species’ close relatives to learn what its ancestors may have been like. Explain how this suggestion anticipates recent methods, such as phylogenetic bracketing and the use of outgroups in cladistic analysis.

SCIENTIFIC INQUIRY • DRAW IT (a) Draw a phylogenetic tree based on characters 1–5 in the table below. Place hatch marks on the tree to indicate the origin(s) of characters 1–6. (b) Assume that tuna and dolphins are sister species and redraw the phylogenetic tree accordingly. Use hatch marks to indicate the origin(s) of characters 1–6. (c) Determine how many evolutionary changes are required in each tree. Identify the most parsimonious tree.

In a short essay (100–150 words), explain how genetic information—along with an understanding of the process of descent with modification—enables scientists to reconstruct phylogenies that extend hundreds of millions of years back in time.

SYNTHESIZE YOUR KNOWLEDGE This West Indian manatee (Trichechusmanatus) is an aquatic mammal. Like amphibians and reptiles, mammals are tetrapods (vertebrates with four limbs). Explain why manatees are considered tetrapods even though they lack hind limbs, and suggest traits that manatees likely share with leopards and other mammals (see Figure 26.12b). Discuss how early members of the manatee lineage might have differed from today’s manatees.