Chapter 20: Phylogenies and the History of Life Flashcards
What is a phylogenetic tree, and what do its components represent?
A diagram showing evolutionary relationships among species.
Components:
Branches: Lineages evolving over time.
Nodes: Points where branches split, representing common ancestors.
Taxa: Species or groups at the tips.
Define a clade and provide an example.
A group including an ancestor and all its descendants.
Example: Tetrapods: amphibians, reptiles, birds, mammals.
What is the principle of parsimony in constructing phylogenetic trees?
The tree with the fewest evolutionary changes (mutations, trait shifts) is most likely correct.
What is a bootstrap value, and how is it interpreted?
Percentage indicating how often a node appears in repeated analyses.
Example: 95% = high confidence in that branching point.
How do molecular clocks estimate divergence times between species?
Assume a constant mutation rate over time.
Example: Mitochondrial DNA mutations used to date human-chimp split ~6–7 mya.
Why is ribosomal RNA (rRNA) widely used in molecular phylogenetics?
Conserved across all life forms, allowing comparison of distantly related organisms.
Example: Constructing the ‘tree of life’.
How does horizontal gene transfer (HGT) complicate phylogenetic trees?
Genes transferred between unrelated species create ‘mosaic’ genomes, conflicting with vertical inheritance patterns.
Example: Antibiotic resistance genes in bacteria.
Why might morphological data lead to inaccurate phylogenies?
Convergent evolution leads to similar traits evolving independently.
Example: Wings in bats vs. birds.
Differentiate monophyletic, paraphyletic, and polyphyletic groups.
Monophyletic: Ancestor + all descendants (e.g., Primates).
Paraphyletic: Ancestor + some descendants (e.g., Reptiles excluding birds).
Polyphyletic: No common ancestor (e.g., Warm-blooded animals: birds and mammals).
How do fossils aid in phylogenetic analysis?
Provide calibration points for molecular clocks and evidence of extinct lineages.
Example: Archaeopteryx linking dinosaurs and birds.
How does endosymbiotic theory explain eukaryotic organelle origins?
Mitochondria/Chloroplasts: Engulfed prokaryotes evolved into organelles, supported by circular DNA and bacterial-like ribosomes.
How do phylogenies inform conservation efforts?
Prioritize species with unique genetic heritage.
Example: Coelacanth as a ‘living fossil’.
How did the HIV phylogeny trace the virus’s origin?
Compared HIV strains to SIV in chimpanzees, pinpointing cross-species transmission in early 20th-century Africa.
What does the ‘tree of life’ reveal about biodiversity?
Three domains: Bacteria, Archaea, Eukarya; highlights horizontal gene transfer’s role in early evolution.
What is maximum likelihood in phylogenetic analysis?
Uses statistical models to find the tree most likely to produce observed data under evolutionary assumptions.
Example: Jukes-Cantor model.
