Study Notes
Cladistics is a method used to classify organisms based on common ancestry and evolutionary relationships. It involves constructing cladograms, which are tree diagrams showing the probable sequence of divergence in clades.
- Clade — A group of organisms that have evolved from a common ancestor. Example: Birds and non-avian dinosaurs form a clade called dinosauria.
- Cladogram — A tree diagram that shows the most probable sequence of divergence in clades. Example: A cladogram can show the relationship between birds and reptiles.
- Molecular Clock — A method that uses the number of differences in DNA sequences to estimate the time since two species diverged from a common ancestor. Example: The human-chimpanzee split is estimated to have occurred 5 million years ago.
- Homologous Structures — Similar structures in different species due to shared ancestry. Example: The human arm and chicken wing are homologous structures.
- Analogous Structures — Similar structures in different species due to convergent evolution. Example: The human eye and the octopus eye are analogous structures.
Exam Tips
Key Definitions to Remember
- Clade: A group of organisms evolved from a common ancestor.
- Cladogram: A tree diagram showing evolutionary relationships.
- Molecular Clock: A method to estimate divergence times using DNA differences.
- Homologous Structures: Similar due to shared ancestry.
- Analogous Structures: Similar due to convergent evolution.
Common Confusions
- Confusing homologous and analogous structures.
- Misinterpreting the nodes on a cladogram as current species rather than common ancestors.
Typical Exam Questions
- What is a clade? A group of organisms that have evolved from a common ancestor.
- How can DNA sequences be used in cladistics? DNA sequences can provide evidence for evolutionary relationships and estimate divergence times.
- What is the difference between homologous and analogous structures? Homologous structures are similar due to common ancestry, while analogous structures are similar due to convergent evolution.
What Examiners Usually Test
- Understanding of how cladograms represent evolutionary relationships.
- Ability to distinguish between homologous and analogous traits.
- Application of the molecular clock concept to estimate divergence times.