A 3.2.4 - biology study for cladistics test

What is the definition of a clade?

A group of organisms that have evolved from a common ancestor, including any species that have since become extinct.

Using the "scissors analogy" from the slides, how can you identify a complete clade on a cladogram?

• If you cut a single branch of a cladogram, all the nodes and taxa that are cut off together form a single clade.

True or False: A single species can only belong to one specific clade.

False. Every species belongs to multiple clades that are nested inside increasingly larger clades (e.g., humans are part of the hominin, primate, and mammalian clades).

What is considered the most objective type of evidence for placing organisms into a clade?

• Molecular sequence homologies, which include DNA base sequences or protein amino acid sequences (like Cytochrome C).

What are morphological homologies?

• Similarities in the size and shape of anatomical structures (such as the pentadactyl limb) shared by different organisms.

In what specific scenario is morphological homology the only available evidence to classify organisms?

When species have become extinct and the only remaining evidence comes from fossils.

What is the ideal approach when scientists gather data to construct a highly reliable cladogram?

• They should combine multiple sources of evidence (both molecular and morphological) whenever possible.