Question

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Cladistics & Homology • What does it mean when we say a cladogram depicts a “hypothesis...

Cladistics & Homology

• What does it mean when we say a cladogram depicts a “hypothesis of genealogical relationships between taxa”?

• What part of the “anatomy” of a cladogram represents a historical speciation event?

• Define synapomorphy and plesiomorphy. How can one character be both?

• What kind of characters are useful in building a cladogram?

• Why are characters found in only one taxon not informative in phylogeny reconstruction?

• What is the difference between a monophyletic, polyphyletic and paraphyletic group?

Which of these ps is/are “accepted” in cladistics?

• Define homology

• Why is homology considered the central concept of comparative biology?

• What is the relationship between synapomorphy, homology, and monophyly?

• What is one similarity and one difference between traditional homology and serial homology?

• What is the term for similarity due to convergent evolution?

• If presented with two taxa that have a similar structure, what evidence would you look for to determine if those structures were homologous?

• Given a cladogram, could you determine which taxa were more closely related?

• Given multiple cladograms, could you determine which depicted equivalent hypotheses of relationships?

• What is the principle of maximum parsimony, and how would you determine which of two cladograms was more parsimonious?

• Why is it incorrect to refer to any living taxon as being primitive? What does “basal” mean in terms of phylogenies?

Solutions

Expert Solution

1. It means that a cladogram is a diagramatic depiction of phylogenetic relation between different taxa.

2. The nodes of a cladogram, where branching off occurs depicts a historical speciation event.

3. Synapomorphy: a characteristic present in an ancestral species and shared exclusively by its evolutionary descendants.

Plesiomorphy: An evolutionary trait that is homologous within a particular group of organisms but is not unique to members of that group (compare apomorphy) and therefore cannot be used as a diagnostic or defining character for the group. For example, vertebrae are found in zebras, cheetahs, and orang-utans, but the common ancestor in which this trait first evolved is so distant that the trait is shared by many other animals. Therefore, possession of vertebrae sheds no light on the phylogenetic relations of these three species.

4. Genetic data as well as conserved morphological data can be useful in building a cladogram.

5. Because they do not establish relationship of that taxon with other taxa.

6.

7. Homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa. eg. human arm, cheetah front leg and bat-wing.


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