A 3.2 classification + cladistics

What is the purpose of biological classification?

To organize organisms hierarchically from broad to specific groups.

List the main hierarchical levels of classification.

Domain → phylum → kingdom → species.

How does classification help identify organisms?

Traits (like fur) indicate taxonomic groups and predict features.

Why can classification be difficult?

Species diverge slowly, making boundaries unclear.

Give an example of clear vs blurry species differences.

Salamander vs frog = clear; human populations = blurry.

Why does classification allow predictions about traits?

Species inherit traits from common ancestors.

What is a clade?

A group of organisms evolved from a common ancestor.

What unifies all clades regardless of size?

All clades share a common ancestor.

What data is increasingly used to form clades accurately?

DNA base sequence comparisons.

When is morphology used instead of DNA?

When DNA cannot be obtained (e.g., extinct species).

What does the molecular clock estimate?

Divergence time based on DNA mutation differences.

Why is the molecular clock limited?

Mutation rates vary between species.

Name three factors affecting mutation rates.

Population size, selective pressure, generation time.

Is the molecular clock precise?

No — it gives approximate timing only.

What does modern cladistics use to compare DNA?

Computer software.

What is the parsimony criterion?

Choosing the evolutionary path with the fewest mutations.

Why doesn’t parsimony prove exact evolutionary history?

It shows the most likely path, not guaranteed truth.

What does a cladogram show?

Evolutionary relationships based on shared ancestry.

What is a terminal branch?

A current species or entire clade.

What is a node?

A divergence point representing an ancestral species.

What is the root of a cladogram?

The common ancestor of all organisms shown.

What was classification based on before the 1990s?

Morphological traits.

How did DNA sequencing change taxonomy?

It revealed many organisms were grouped incorrectly by appearance.

What happened to the figwort family after DNA analysis?

Many species were reassigned; the family dropped from 8th to 36th largest.

What are the three domains of life?

Archaea, Bacteria, Eukarya.

What discovery led to separating prokaryotes into Archaea and Bacteria?

Ribosomal RNA analysis

Why is rRNA important in taxonomy?

It reveals deep evolutionary relationships and supports domain-level classification.