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Ch. 25 - Phylogenies and the History of Life
Chapter 24, Problem 2

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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Understand the terms: A synapomorphy is a characteristic shared by two or more taxa that is inherited from their most recent common ancestor. Phylogenetic analysis involves the study of the evolutionary relationships among groups of organisms.
Analyze the statement: The statement claims that only traits that are present and derived (newly evolved traits that distinguish a clade) can be used as synapomorphies in phylogenetic analysis, implying that absent traits cannot serve this purpose.
Consider exceptions: Think about cases where the absence of a trait could be a derived condition if the ancestor had the trait and the derived taxa lost it. This absence could potentially be considered a synapomorphy if it provides information about evolutionary relationships.
Evaluate the relevance of absent traits: Determine if the absence of a trait can be reliably identified as a derived condition rather than a primitive condition (a trait that was absent in the ancestor). This is crucial for its use in phylogenetic analysis.
Conclude the critique: While the statement holds in scenarios where the absence of a trait cannot be clearly identified as a derived condition, there are cases where an absent trait can be a synapomorphy if it represents a derived state that helps clarify evolutionary relationships among taxa.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Synapomorphy

A synapomorphy is a shared derived trait that is used to infer evolutionary relationships among organisms. It is a characteristic that is present in an ancestor and its descendants but absent in more distant relatives. In phylogenetic analysis, synapomorphies help define clades, which are groups of organisms that share a common ancestor.
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Phylogenetic Analysis

Phylogenetic analysis is a method used to study the evolutionary relationships between different species or groups. It involves constructing a phylogenetic tree, which visually represents these relationships based on shared traits, genetic data, or other characteristics. The accuracy of this analysis relies heavily on identifying synapomorphies and understanding the evolutionary history of the organisms involved.
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Building Phylogenetic Trees Example 2

Clade

A clade is a group of organisms that includes an ancestor and all its descendants, forming a branch on the tree of life. Clades are defined by synapomorphies, which are traits that are unique to that group. Understanding clades is essential for interpreting phylogenetic trees and recognizing how different species are related through common ancestry.
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Related Practice
Textbook Question

Choose the best definition of a fossil. a. a rock that contains information about an organism b. a bone, tooth, shell, or other hard part of an organism that has been preserved c. any trace of an organism that lived in the past d. any part of a dead organism

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Textbook Question

Why does the presence of extinct forms and transitional features in the fossil record support the pattern component of the theory of evolution by natural selection? Select True or False for each statement. T/F It supports the hypothesis that individuals change over time. T/F It supports the hypothesis that weaker species are eliminated by natural selection. T/F It supports the hypothesis that species evolve to become more complex and better adapted over time. T/F It supports the hypothesis that species change over time.

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Textbook Question

Which of the following best characterizes an adaptive radiation? a. Descendant species occupy a large geographic area. b. A single lineage diversifies rapidly, and descendant species occupy many habitats and ecological roles. c. Natural selection is particularly intense, because disruptive selection occurs. d. Species recover after a mass extinction.

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Textbook Question

Which of the following is an example of homoplasy? a. hair in humans and fur in mice b. astragalus ankle bones in hippos and deer c. Hox genes in humans and flies d. streamlined bodies in dolphins and ichthyosaurs

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Textbook Question

What important assumption does parsimony make when assessing which phylogenetic tree is most accurate? Why was parsimony misleading in the case of the astragalus during the evolution of artiodactyls?

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