Classification and cladistics

Why is the classification of organisms important?

What are the difficulties classifying organisms into a hierarchy using morphology and in determining what a species is?

Morphology: organisms with similar charactersitics don’t mean they share a common ancestor. explained by convergent evolution.

Determing species: the point at which two populations are considered two species is subjective and hard to determine

What methods overcome the issues with classifying organisms?

Using DNA&RNA base sequences to classify organisms into groups.

What are the pros of classifying organisms based on evolutionary relationships.

natural and biologically meaningful way to group them into clades based on common ancestry

Reflects the process of evolution, such as branching patterns of speciation

How can mutations be used as a molecular clock?

What factors limit the effectiveness of molecular clocks?

Limit: assumes mutation rate is constant

Mutations may have been reversed

Why is using observable characteristics to construct cladograms bad?

Similarities in charactersitics may be misleading as they may not be result of common ancestry but rather convergent evolution.

What evidence is now used to prove what clade a species belongs to?

How can comparing base sequences demonstrate the degree of evolutionary divergence?

DNA and RNA base sequences

Number of differences in DNA and RNA base sequences showcases how similar or different species are.

In a cladogram, whats a branch, node, and root

Branch: existing species

node: hypothetical common ancestor

root: most ancient common ancestor

What does the number of nodes say about species relatedness?

more nodes between species means they’re more distantly related.

What are the 3 domains all organisms are classifeid into?

Archaea, eubacteria, eukarya