What is a cladogram? How does the classification system work? In this IBDP Biology blog, we will learn what a clade is, and the traits that are considered when making the following classifications.
What is a Clade?
Clade: Group of organisms that have evolved from a common ancestor
These groups of species can be identified by looking for shared characteristics
Clades include all the species alive today and species that have evolved and became extinct
- Species that have a recent common ancestor are expected to have few amino acid sequence differences
- Species that have some similarities but diverged from a common ancestor a long time ago are expected to have many differences
Molecular Clock
Mutations occur at a relatively constant rate so they can be used as molecular clocks
Molecular clocks: The number of genetic differences can predict how long ago two species diverged
The larger the number of differences between two species the longer the time since they diverged from a common ancestor
If the base sequences are similar then few mutations have occurred which means the species only diverged recently
LIMITATIONS
- Different genes or proteins may change at different rates
- The rate of change for a certain gene may differ between two groups of organisms
- May question the accuracy of early predictions based on more recent findings
Homologous vs Analogous Traits
Homologous structures: Structures that are similar because of similar ancestry
Might have different functions
Analogous structures: Structures that are similar because of convergent evolution [different organisms independently evolve similar traits] but evolved independently
Same structure and functions such as human and octapus eyes
That's the end!
Drafted by Venetia (Biology)