Ch 20: Phylogeny

Question 1

Understand that phylogenetic trees are hypotheses of evolutionary relationships

Answer 1

• Phylogenetic trees are hypotheses of evolutionary relationships between different groups of organisms
• Animal diversity is organized following a nested hierarchy of groups within groups according to HYPOTHESIZED evolutionary relationships
• Phylogenetic analysis are based on finding features, characters, that species have in common because these characters are inherited from a common ancestor (on the same lineage).

Question 2

Describe how phylogenetic trees are constructed and what type of data is used

Answer 2

Many different types of data can be used to construct phylogenetic trees, including morphological data, such as structural features, types of organs, and specific skeletal arrangements; and genetic data, such as mitochondrial DNA sequences, ribosomal RNA genes, and any genes of interest.

Question 3

Define homologous, analogous, synapomorphy, parsimony

Answer 3

• Homologous: Common descent from an ancestor that had that character
• Analogous: Convergent evolution, in which the character evolved independently in two separate groups (Homoplasies)
• Synapomorphy: a characteristic present in anancestralspecies and shared exclusively (in more or less modified form) by itsevolutionarydescendants.
• Parsimony: In terms of tree-building, that means that, all other things being equal, the best hypothesis is the one that requires the fewest evolutionary changes.

Question 4

Difference between Homologues and Synapomorphies

Answer 4

All homologues are synapomorphies, but not vice- versa. Absence of an anatomical element, for instance, can be a taxonomical synapomorphy but not a homology, because homologues are positive anatomical parts.

Question 5

Explain why homologous traits are useful for constructing phylogenetic trees, but homoplasies (analogous traits) are not

Answer 5

Homoplasies (analogous traits) are not useful in constructing a phylogenetic tree because homoplasy helps explain how unrelated species can come to receive similar biological traits.

Question 6

Explain what the different parts of the phylogenetic tree represent

Answer 6

• A clade (branches) is the basic unit of phylogenetic grouping of species.
  
  • Includes: ancestral lineage and all species that descend from that lineage.
• A ‘taxon’ is a group of organisms at any hierarchical rank, such as a family, genus, or species.
  
  • Basal taxon: In a specified group of organisms, a taxon whose evolutionary lineage diverged early in the history of the group
• Sister Group: the closest relative(s) of another given unit in an evolutionary tree.

Question 7

Define monophyletic, paraphyletic, polyphyletic

Answer 7

• Monophyletic: A taxon containing a common ancestor and all of its descendants
• Paraphyletic: A taxon containing a common ancestor but not all of its descendants
• Polyphyletic: A taxon containing groups of species with different common ancestors

Question 8

Difference between phylogenetic tree and cladogram

Answer 8

• A phylogenetic tree shows evolutionary and genetic distance while a cladogram displays related characteristics.

Question 9

Notes on evolution

Answer 9

• All organisms have equally long evolutionary histories. It cannot be said that one species is more evolved than the other as there is no scale to measure evolution. The destination of evolution is not known to tell which species has evolved maximally and is near to the destination. Every species has its own evolution pathway, and they adapt accordingly.