Introduction to cladogram construction answer key

Lab 2 Introduction to Cladistics
Subject
Science

Question Description
Complete Lab 2 Introduction to Cladistics (Only Pages 6-15) of the attached lab. online simulation lab.

Bio104 Laboratory – Student’s Manual John Jay College, C.U.N.Y Lab #2: Introduction to Cladistics I. Cladistics and the Classification of Life’s Diversity • Humans are always classifying and organizing things. F o r information to be shared with others in a meaningful way, it must be organized in a meaningful way. Imagine how unhelpful a phone book would be if it weren’t alphabetized! • The task of classifying and organizing living things (organisms) on earth belongs to scientists called systematists. The field of systematics exists to provide the order and organization for our extensive knowledge of the living world. • Although there are many logical ways to classify organisms, a biologically useful scheme of classification is one which not only facilitates the identification of individual species, but also explains evolutionary relationships among species. One aspect of systematics, taxonomy, deals with naming and classification; a second aspect of this field, phylogenetics, deals with evolutionary relationships among organisms. • In Laboratory 1, we defined evolution as the changes in genetic composition over time which drive the origin and extinction of species (through processes such as geographic or reproductive isolation and adaptation). A species, then, may be defined as a group of organisms which shares a “genetic composition” inherited from a common ancestor. • Scientists use branching diagrams called cladograms to communicate how groups of organisms are classified and how they are evolutionarily related. 1 Bio104 Laboratory – Student’s Manual John Jay College, C.U.N.Y II. Introduction to the Laboratory Exercise • In this Laboratory, we will learn how to “read” (interpret) cladograms. • In this Laboratory, we will learn how to make a “character table” using physical traits shared by a group or groups of organisms. • In this Laboratory, we will learn how to build a cladogram based on the character table that we constructed. III. Key Terms for this Lab (Except where noted, all definitions are from http://www.ucmp.berkeley.edu/glossary/gloss1phylo.html. Comments in italics have been added for clarification.) • Phylogeny -- The evolutionary relationships among organisms; the patterns of lineage branching produced by the true evolutionary history of the organisms being considered. Note: a phylogeny may be represented by a phylogenetic tree or a cladogram. • Cladogram. A diagram which depicts a hypothetical branching sequence of lineages leading to the taxa under consideration. The points of branching within a cladogram are called nodes. All taxa occur at the endpoints of the cladogram. (Note: branching is dichotomous, meaning that a lineage can branch only into two new lineages. The two new lineages are called “sister groups”. More than two lineages are sometimes seen in a cladogram branching from a single node, but this case indicates that there is not enough information available to know how the lineages diverged). • Clade. A monophyletic taxon; a group of organisms which includes the most recent common ancestor of all of its members and all of the descendants of that most recent common ancestor. From the Greek word "klados", meaning branch or twig. • Taxon. Any named group of organisms, not necessarily a clade; a taxon may be designated by a Latin name or by a letter, number, or any other symbol; taxa- pl. • Character. Heritable trait possessed by an organism; characters are usually described in terms of their states, for example: "hair present" vs. "hair absent," where "hair" is the character, and "present" and "absent" are its states. • Ancestor. Any organism, population, or species from which some other organism, population, or species is descended by reproduction. • Synapomorphy. A character which is derived (that is, it differentiates a clade which branched from an earlier lineage), and because it is shared by the taxa under consideration, is used to infer common ancestry. (Note: also called a shared derived character) • Plesiomorphy. A primitive character state for the taxa under consideration (that is, it is a trait that arose before the clade branched from an earlier lineage; also called an ancestral character) 2 Bio104 Laboratory – Student’s Manual John Jay College, C.U.N.Y • Outgroup. in a cladistic analysis, (a) taxon… which is hypothesized to be less closely related to each of the taxa under consideration than any are to each other. • Monophyletic group. Term applied to a group of organisms which includes the most recent common ancestor of all of its members and all of the descendants of that most recent common ancestor. A monophyletic group is also called a clade. • Paraphyletic group. Term applied to a group of organisms which includes the most recent common ancestor of all of its members, but not all of the descendants of that most recent common ancestor. • Polyphyletic group. Term applied to a group of organisms which does not include the most recent common ancestor of those organisms; the ancestor does not possess the character shared by members of the group. • Parsimony. Refers to a rule used to choose among possible cladograms, which states that the cladogram implying the least number of changes in character states is the most likely. IV. Practice Reading and Building Cladograms Instructions 1. The following exercises are adapted from http://www.geol.umd.edu/~jmerck/tassite/eltsysex/sysanswers.html#q4c We thank John W. Merck, Jr. of the University of Maryland, who developed them. 2. You will work on the questions in pairs for 30 minutes. Following that, we will go over the answers to the questions as a class. Part I: Reading cladograms A. Cladograms usually represent evolutionary events which happened in sequence. These events,