Question

1. Why are clades “supported” by one or more synapomorphy? We expect the synapomorphy to be present in all the members of the clade defined by the trait – but the character might be highly modified, or present only a brief developmental stage. [Sometimes the trait is lost altogether, a situation we call being “secondarily lost”]

2. What kinds of traits are used to construct phylogenies? What is the key feature of a trait that may be used to construct a phylogeny?
3. Remember the examples for applications of phylogenic analyses: HIV forensics case, swordfish evolution.
4. Make sure you are very comfortable with these terms: monophyletic, polyphyletic, paraphyletic. Which is used for the construction of phylogenetic trees, and why? Why are the others still used in various applications?

5. Understanding the physical origins and dynamics of Earth helps us understand the origin of life and show how life also influences the makeup of the physical environment. Be able to explain the key features of each eon/period on the diagram on this page: Hadean, Archaean, Proterozoic, Phanerozoic. What does the Precambrian refer to?

Answer 1

Answer:

1):

• Synapomorphies are (morphological, molecular, or behavioral) characters shared by a group of taxa due to their inheritance from a common ancestor.
• Synapomorphies thus constitute evidence for historical relationships and their associated hierarchical structure.
• For example, the cladogram
• Cladograms, phylogenetic trees that depict evolutionary relationships among a set of taxa, are one of the most powerful predictive tools in modern biology. They are
• usually depicted in one of two formats—tree or ladder. Previous research (Novick and Catley 2007) has found that college students have much greater difficulty understanding a cladogram’s hierarchical structure when it is depicted in the ladder format.
• Such understanding would seem to be a prerequisite for successful tree thinking.
• The present research examined the effect of a theoretically guided manipulation—adding a synapomorphy on each branch that supports two or more taxa—on students’ understanding of the hierarchical structure of ladder cladograms.
• Synapomorphies are characters shared by a group of taxa due to inheritance from a common ancestor.
• Thus, their depiction on a cladogram may facilitate the understanding of evolutionary relationships.
• Students’ comprehension was assessed in terms of success at translating relationships depicted in the ladder format to the tree format. T
• results indicated that adding synapomorphies provided powerful conceptual scaffolding that improved comprehension for students with both weaker and stronger backgrounds in biology.
• For stronger background students, the benefit of adding synapomorphies to the ladders was comparable to that of approximately two hours of instruction in phylogenetics that emphasized the ladder format.
• Cladograms are phylogenetic trees that depict evolutionary relationships among a set of taxa in terms of nested levels of common ancestry.
• Synapomorphies are (morphological, molecular, or behavioral) characters shared by a group of taxa due to their inheritance from a common ancestor.
• Synapomorphies thus constitute evidence for historical relationships and their associated hierarchical structure.
• For example, the cladogram in shows the evolutionary relationships, supported by synapomorphies, among genera of Mollusca.
• Cladograms are one of the most powerful predictive tools in modern biology. U
• monophyly—groupings comprising all descendent taxa and their most recent common ancestor (a.k.a. clades)—to organize and make sense of the 3.5 billion year history of life on Earth, they provide a conceptual framework for basic and applied biology in fields as disparate as conservation, ecology, behavior, molecular biology, epidemiology, and pharmacology .G
• the importance of cladograms in biology, it is not surprising that a number of researchers and educators have called for the inclusion of tree thinking in biology curricula for both biology majors and nonmajors, as well as at the high school level.

2):

• Tobuild a phylogenetic tree such as the one to the right, biologists collect data about the characters of each organism they are interested in.
• Characters are heritable traits that can be compared across organisms, such as physical characteristics (morphology), genetic sequences, and behavioral traits.
• Phylogenetic trees represent hypotheses about the evolutionary relationships among a group of organisms.
• A phylogenetic tree may be built using morphological (body shape), biochemical, behavioral, or molecular features of species or other groups.
• In building a tree, we organize species into nested groups based on shared derived traits (traits different from those of the group's ancestor).
• The sequences of genes or proteins can be compared among species and used to build phylogenetic trees.
• Closely related species typically have few sequence differences, while less related species tend to have more.

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