Cycle 9 Flashcards
Evolutionary Relationships
Q: What is the direction of time in phylogenetic trees?
A: Time moves from the base to the tips of the tree.
Q: What is a clade in phylogenetic classification?
A: A clade includes all descendants of a most recent common ancestor (MRCA).
Q: What type of groups are recognized in cladistic classification?
A: Only monophyletic groups (clades), where members are more closely related to each other than to any outside the group.
Q: Why are traits like autapomorphies and symplesiomorphies not useful in phylogenetic analysis?
Autapomorphies are unique and do not reveal relationships between taxa.
Symplesiomorphies are ancestral and already present in the MRCA, so they are not informative.
Q: What is a synapomorphy?
A: A shared, derived trait present in the MRCA of a subset of taxa but not the MRCA of the entire group. It reveals evolutionary relationships.
Q: What is an ancestral trait?
- A trait that was present in the most recent common ancestor (MRCA) of a group.
- It is inherited from earlier ancestors without significant change.
- Example: The backbone in vertebrates is ancestral because it was present in the MRCA of all vertebrates.
Q: What is an derived trait?
- A trait that has evolved after the MRCA of a group.
- It is new or modified compared to the ancestral state.
- Example: Feathers in birds are derived because they evolved after the MRCA of all amniotes (reptiles, birds, and mammals).
Q: What is the key difference between ancestral and derived traits?
- Ancestral traits are “old” traits that were already present in earlier ancestors.
- Derived traits are “new” traits that arose in a particular lineage after divergence from a common ancestor.
Q: How does outgroup comparison help in phylogenetics?
A: It helps determine if a trait is ancestral or derived based on whether it is present in the outgroup and ingroup.
Q: What is homology?
A: A similarity due to common ancestry.
Q: What is homoplasy, and how can it mislead phylogenetic analysis?
A: Homoplasy is misleading similarity or dissimilarity, such as convergent or divergent evolution, which does not reflect common ancestry.
Q: What traits were identified as synapomorphies in the ingroup example (chicken, bat, chipmunk)?
A:
Wings (shared, derived trait in some).
Fur (shared, derived trait in some).
Lactation (shared, derived trait in some)
