Textbook Question
Critique the following statement: The absence of a trait cannot be used as a synapomorphy in phylogenetic analysis; only shared derived traits that are present in the clade can be used.
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25. Phylogeny
Phylogeny
0:57 minutesProblem 4
Textbook Question
Three living species, X, Y, and Z, share a common ancestor, T, as do extinct species U and V. A grouping that consists of species T, X, Y, and Z (but not U or V) makes up
a. A monophyletic taxon
b. An ingroup, with species U as the outgroup
c. A paraphyletic group
d. A polyphyletic group
Verified step by step guidance1
Understand the definitions of the different types of taxonomic groups: Monophyletic, Paraphyletic, and Polyphyletic. A monophyletic group includes a common ancestor and all its descendants. A paraphyletic group includes a common ancestor and some, but not all, of its descendants. A polyphyletic group includes species with different ancestors.
Identify the common ancestor in the problem. Here, species T is the common ancestor of species X, Y, and Z, as well as extinct species U and V.
Determine which species are included in the grouping. The grouping consists of species T, X, Y, and Z.
Evaluate whether the grouping includes all descendants of the common ancestor T. Since species U and V are descendants of T but are not included in the grouping, this grouping does not include all descendants.
Based on the definitions and the evaluation, determine which type of taxonomic group the grouping represents. Since the grouping does not include all descendants of the common ancestor T, it is a paraphyletic group.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Monophyletic Taxon
A monophyletic taxon, also known as a clade, includes an ancestor and all of its descendants. This grouping is characterized by shared evolutionary history and is used to represent a complete lineage. In the context of the question, a monophyletic taxon would include species T, X, Y, and Z, as they all share a common ancestor without excluding any descendants.
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Paraphyletic Group
A paraphyletic group consists of an ancestor and some, but not all, of its descendants. This type of grouping excludes one or more lineages that share the same ancestor. In the question, if species U and V are excluded from the group containing T, X, Y, and Z, it forms a paraphyletic group because it does not include all descendants of the common ancestor T.
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Polyphyletic Group
A polyphyletic group is formed from organisms that do not share an immediate common ancestor, often grouped based on similar characteristics rather than evolutionary history. This type of grouping is not ideal for reflecting evolutionary relationships. In the question, a polyphyletic group would not apply to T, X, Y, and Z, as they share a common ancestor, unlike a polyphyletic grouping.
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