Phylogenetic Trees Evolution Lecture 6

A set of Q&A flashcards covering key concepts from Phylogenetic Trees lecture notes, including clades, rooted/unrooted trees, nodes, branches, ancestral vs derived traits, outgroups, relatedness, and examples of mammal lineages.

What is the primary purpose of phylogenetic trees (cladograms) in evolution?

They are essential for studying evolution and emphasize the branching nature of evolution—a bush, not a ladder.

What is a clade?

A group that includes a common ancestor and all its descendants; clades can be nested within other clades.

What is the difference between rooted and unrooted phylogenetic trees?

Rooted trees have a root and show the direction of time (often using an outgroup); unrooted trees show relationships without a specified temporal direction.

What is the purpose of an outgroup in a rooted tree?

To root the tree and provide information about ancestral vs. derived characters.

What do nodes represent in a phylogenetic tree?

The common ancestor of a clade and the points where lineages diverge.

What do branches represent in a phylogenetic tree?

The evolutionary changes that occurred over time as new groups evolved.

What are ancestral and derived characters?

Ancestral characters are traits present in the common ancestor; derived characters are traits that appear in descendants.

What does a cladogram emphasize about time?

The branching pattern rather than the exact timing of when branches occurred; branches may not be time-scaled.

What does it mean that the tree can 'spin' around the nodes?

The order of the tips is arbitrary; rotating around nodes does not change relationships.

What is meant by nested clades and the Linnaean hierarchy?

Clades can be contained within larger clades, illustrating a hierarchical, nested classification.

What is a sister group in a phylogenetic tree?

The closest relative to a clade; they share a most recent common ancestor not shared with other groups.

Why use an outgroup to root a tree?

To root the tree and infer ancestral vs. derived characters across the ingroup.

Are humans more closely related to cats or salamanders?

Cats — humans share a more recent common ancestor with cats than with salamanders.

Are humans more closely related to birds or iguanas?

Birds — humans are more closely related to birds than to iguanas.

Are you more closely related to one cousin than another?

No — you are equally related to all your first cousins.

What does it mean when branch lengths are not scaled to time?

Branch lengths do not reflect actual time; only the branching pattern reflects relationships.

What does 'You can include as much or as little as you want as long as the branching is correct' mean?

You can include or exclude taxa as long as the overall branching relationships are accurate.

What are monotremes?

Egg-laying mammals (e.g., platypus and echidnas); they are among the most primitive mammals.

What are marsupials?

Mammals with prolonged lactation and a pouch, typically with a shorter gestation period.

What are eutherians (placental mammals)?

Mammals with a placenta and longer gestation, followed by lactation (e.g., most mammals).

What do synapsids and diapsids refer to?

Major amniote lineages: Synapsids include mammals; Diapsids include lepidosaurs (lizards) and archosaurs (crocodilians and birds).

What does common ancestry tell us about relatedness?

Relatedness is determined by how recently lineages share a common ancestor; closer relatives have more recent common ancestors (e.g., siblings vs cousins).

What common evolutionary misconception does the 'progression' slide address?

Evolution is not a linear progression from 'more simple' to 'more complex'; it is branching with diverse lineages.

What are the three major mammal lineages mentioned, and a key trait for each?

Monotremes (egg-laying mammals, e.g., platypus); Marsupials (pouch and prolonged lactation); Eutherians (placental mammals with longer gestation).