Topic 1.7: Classification and Cladistics (HL) Questions

State the term used for a group that consists of a common ancestor together with all of its descendants.

Which phrase best defines a clade?

State one named example of a group of organisms that has been reclassified because of cladistic evidence, and give the type of group it had wrongly been.

On a cladogram, what does a node (branch point) represent?

Modern cladograms are built mainly from which type of evidence?

Two groups on a cladogram are MOST closely related when their branches meet at which point?

Two species' DNA base sequences for the same gene show MANY differences. What does this suggest about the two species?

What does the root of a cladogram represent?

Define the term monophyletic group.

Cladistics groups organisms primarily on the basis of which type of evidence?

State what a single node (branch point) on a cladogram represents.

What is a clade?

State two types of molecule whose sequences can be compared between species to provide molecular evidence of how closely they are related.

The amino-acid sequence of the same protein in a test species is compared with three other species, giving 6 differences with species J, 19 differences with species K, and 31 differences with species L. Deduce the order of the three species from the most closely to the most distantly related to the test species, and justify your ranking.

Outline why two species that diverged from a common ancestor long ago show more sequence differences than two species that diverged recently.

Distinguish between using molecular evidence and using physical (morphological) features to determine how closely two species are related.

A cladogram of several frog species, originally drawn from body features, is later rearranged after DNA sequence data is collected. Explain why a cladogram is described as a hypothesis and can be revised in this way.

Until recently a particular insect species was placed in genus A alongside several similar-looking species. A molecular (DNA) study then showed its closest relatives actually belong to genus B, and the species was moved to genus B. Explain why this reclassification was carried out.

Outline the chain of reasoning by which a conflict between DNA evidence and a traditional classification leads to organisms being reclassified.

In cladistics, organisms are grouped into clades. Define the term clade, and explain why modern biologists aim for a natural classification rather than an artificial one.