Study Notes
Cladistics is a method of classifying organisms based on common ancestry and evolutionary relationships. It uses cladograms to represent these relationships visually.
- Clade — A group of organisms that have evolved from a common ancestor.
Example: Birds, non-avian dinosaurs, and ancestral species forming the clade dinosauria. - Cladogram — A tree diagram that shows the most probable sequence of divergence in clades.
Example: A cladogram showing the relationship between birds and reptiles. - Molecular Clock — A method that uses the number of differences in DNA or protein sequences to estimate the time since two species diverged.
Example: Human and chimpanzee split approximately 5,000,000 years ago. - Homologous Structures — Structures that are similar due to shared ancestry.
Example: The pentadactyl limb in humans and birds. - Analogous Structures — Structures that are similar due to convergent evolution, not common ancestry.
Example: The human eye and the octopus eye.
Exam Tips
Key Definitions to Remember
- Clade: A group of organisms evolved from a common ancestor.
- Cladogram: A diagram showing evolutionary relationships.
- Molecular Clock: A technique to estimate divergence time using DNA differences.
- Homologous Structures: Similar structures due to common ancestry.
- Analogous Structures: Similar structures 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 molecular clocks be used in cladistics? By using DNA sequence differences to estimate the time since species diverged.
- What is the difference between homologous and analogous structures? Homologous structures are due to common ancestry, while analogous structures are due to convergent evolution.
What Examiners Usually Test
- Understanding of how to interpret cladograms.
- Ability to distinguish between homologous and analogous traits.
- Knowledge of how molecular evidence supports evolutionary relationships.