Chapter 19: Taxonomy, Systematics, and Phylogeny AP Curriculum Alignment Chapter 19 expands on the topics of phylogenies and cladograms, which are important to Big Idea 1. In order for students to understand how phylogeny or cladograms are constructed, an understanding of the taxonomic groupings of organisms is essential. Several Learning Objectives require that students be able to make connections about similarities across domains so students must understand what the three domains are and what characteristics set them apart from each other. The same lines of evidence that are used to establish evolutionary relatedness are also used to determine how to classify an organism. These lines of evidence include the fossil record, embryology, morphology, and molecular evidence. Chapter 19 includes a short history of human attempts at classification. The relatively recent changes to the system of classification include the formation of three domains. This should help students realize the dynamic nature of biology. ALIGNMENT OF CONTENT TO THE CURRICULUM FRAMEWORK Big Idea 1: The process of evolution drives the diversity and unity of life. Enduring understanding (EU) 1.A: Change in the genetic makeup of a population over time is evolution. Essential knowledge 1.A.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics. Essential knowledge 1.B.2: Phylogenetic trees and cladograms are graphical representations (models) of evolutionary history that can be tested. a. Phylogenetic trees and cladograms can represent traits that are either derived or lost due to evolution. To foster student understanding of this concept, instructors can choose an illustrative example such as: Number of heart chambers in animals Opposable thumbs Absence of legs in some sea mammals b. Phylogenetic trees and cladograms illustrate speciation that has occurred, in that relatedness of any two groups on the tree is shown by how recently two groups had a common ancestor. c. Phylogenetic trees and cladograms can be constructed from morphological similarities of living or fossil species, and from DNA and protein sequence similarities, by employing computer programs that have sophisticated ways of measuring and representing relatedness among organisms. d. Phylogenetic trees and cladograms are dynamic (i.e., phylogenetic trees and cladograms are constantly being revised), based on the biological data used, new mathematical and computational ideas, and current and emerging knowledge. Mader, Biology, 12 th Edition, Chapter 19 289
Concepts covered in Chapter 19 also align to the learning objectives that provide a foundation for the course, an inquiry-based laboratory experience, class activities, and AP exam questions. Each learning objective (LO) merges required content with one or more of the seven science practices (SP), and one activity or lab can encompass several learning objectives. The learning objectives and science practices from the Curriculum Framework that pertain to taxonomy, systematics and phylogeny are shown in the table below. Note that other learning objectives may apply as well. LO 1.17 The student is able to pose scientific questions about a group of organisms whose relatedness is described by a phylogenetic tree or cladogram in order to (1) identify shared characteristics, (2) make inferences about the evolutionary history of the group, and (3) identify character data that could extend or improve the phylogenetic tree. LO 1.18 The student is able to evaluate evidence provided by a data set in conjunction with a phylogenetic tree or a simple cladogram to determine evolutionary history and speciation. LO 1.19 The student is able create a phylogenetic tree or simple cladogram that correctly represents evolutionary history and speciation from a provided data set. Key Concepts Summary Systematics and taxonomy Systematic biology is a quantitative science that uses traits of living and fossil organisms to infer the evolutionary relationships among organisms. o Taxonomists classify organisms into natural groups, which are groupings of organisms that represent a shared evolutionary history. o Taxonomists identify, name, and organize biodiversity into groupings with like traits. These groupings are called taxa. o Taxonomists classify organisms based on a hierarchical set of categories: species, genus, family, order, class, phylum, kingdom, and domain. Natural groups are classified using a set of traits and are organized into a family tree that represents the evolutionary history of taxa Modern systemic biologists use characters from the fossil record, comparative anatomy and development, and the sequence, structure, and function of RNA and DNA molecules to construct a phylogeny. Derived traits, or those not found in the common ancestor of a taxonomic group, are the most important traits for clarifying evolutionary relationships. Taxonomists use the pattern of branching in a phylogeny constructed from an analysis of derived traits to classify taxa into natural groups. o Phylogenetic relationships are illustrated via diagrams known as cladograms. o A clade is a grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor. 290 Mader, Biology, 12 th Edition, Chapter 19
Key Terms analogous structures analogy ancestral traits binomial nomenclature chordates clade cladistics cladogram classification common ancestor convergent evolution derived traits diverge domain Archaea domain Bacteria domain Eukarya five-kingdom system homologous structures homology ingroup lineage molecular clock molecular trait outgroup parsimony phylogeny scientific name systematic biology systematics taxonomy Teaching Strategies Class time: Two 45-minute class periods Day 1: Lecture on taxonomy, systematics and phylogenies 25 minutes Activity 1, constructing a cladogram 20 minutes Day 2: Activity 2, taxonomy of seashells 45 minutes Suggested Approaches There are three Learning Objectives that cover cladograms and phylogenies, which is 2 % of the 149 learning objectives. Students have learned about classification for many years and may think that they already know this material. It is very important that they learn how to use data to interpret or prepare a cladogram. Many biologists use the terms cladogram and phylogeny interchangeably even though there are slight variations between the two. It is generally thought that a phylogeny depicts the true evolutionary relatedness among organisms while cladograms are more of a possible depiction of the evolutionary trends. Both phylogenies and cladograms are subject to change as additional information is obtained, particularly molecular details. While students have already worked with phylogenetic trees in the BLAST Lab, the extra practice here will help cement this concept. It is also very important for students to realize that classification can change with additional evidence, such as DNA sequences, is obtained. Mader, Biology, 12 th Edition, Chapter 19 291
Student Misconceptions and Pitfalls Many students think that you can depict all ancestors in a straight line. If you compare their ancestors, which include cousins and aunts and uncles, they will be better able to understand that most ancestries are branching. The dynamic nature of classification will be new to most students. Most students do not realize that as we obtain additional information, an existing phylogeny may be changes. Suggested Activities 1. Activity 1: Constructing a Cladogram Students should use the data in the table below to form a cladogram. They can conduct research to find the meaning of any terms they are not familiar with. Vertebrate Bony Skeleton Four Limbs Amniotic Egg Hair Two Postorbital fenestrae Sharks and YES NO NO NO NO NO relatives Rayfinned YES YES NO NO NO NO fish Amphibians YES YES YES NO NO NO Primates YES YES YES YES YES NO Rodents and Rabbits YES YES YES YES YES NO Crocodiles and relatives Dinosaurs and Birds YES YES YES YES NO YES YES YES YES YES NO YES 1 2 3 4 5 6 292 Mader, Biology, 12 th Edition, Chapter 19
Answer Key Activity 2: Sorting Seashells This online activity directs students to explore principles of taxonomy by sorting seashells according to their morphological characteristics and constructing an evolutionary tree. http://www.hhmi.org/biointeractive/sorting-seashells As students progress through the online exercise, you can enhance the hands-on nature of the activity by drawing the resulting phylogenetic tree on a piece of paper and placing the shell cards on the appropriate branches. Teacher can also use the blackboard to build the consensus phylogenetic tree. Instead of drawing the branches, you could also use masking tape or pieces of string to represent them. Mader, Biology, 12 th Edition, Chapter 19 293
Student Edition Chapter Review Answers Answers to Assess Questions 1. a; 2. d; 3. d; 4. a, b, c; 5. b, c, d, e; 6. a; 7. c; 8. d; 9. a; 10. c; 11. d Answers to Applying the Big Ideas Questions 1. Phylogenetic trees and cladograms can be constructed from morphological similarities to illustrate speciation that has occurred. Relatedness of any two groups on the tree is shown by how recently two groups had a common ancestor. Using the observable traits recorded in the data table, create a simple cladogram that correctly represents the possible evolutionary relationships among molluscs. Mark the shared characters on your model in the appropriate locations. Mantle Single shell Bivalve Torsion Tentacles gland shell Chiton Yes No No No No Clam Yes Yes Yes No No Snail Yes Yes No Yes No Octopus Yes Yes No No Yes Nautilus Yes Yes No No Yes Essential Knowledge Science Practice Learning Objective 1.B.2: Phylogenetic trees and cladograms are graphical representations (models) of evolutionary history that can be tested. 1.1: The student can create representations and models of natural or man-made phenomena and systems in the domain. 1.19: The student is able to create a phylogenetic tree or simple cladogram that correctly represents evolutionary history and speciation form a provided data set. 3 points maximum. Cladogram representation may include (1 point each): Each organism and character from the data table is represented: chiton, clam, snail, octopus, and nautilus, mantle, single shell gland, bivalve shell, torsion, and tentacles. Evolutionary lines of cladogram are discernable and easily followed. Characters are noted on appropriately matched evolutionary lines, NOT at nodes. Mantle clade includes all organisms; Single shell gland clade includes clams, snail, octopus and nautilus. 294 Mader, Biology, 12 th Edition, Chapter 19
Octopus and nautilus form a clade with shared tentacles trait. Clams are the only organism with a bivalve shell and snails are the only organism with torsion character. Answers to Applying the Science Practices Questions Think Critically 1. D 2. L. Polaris 3. L, K, M; This group has more divisions, which indicates more diversity. Mader, Biology, 12 th Edition, Chapter 19 295
Additional Questions for AP Practice 1. Which if the following shaded groups represents a clade? 2. If species A and C have fewer differences between their DNA sequences than species B and D, which of these phylogenetic trees is correct? A B C D A C B D D C B D D C A B 3. Describe characteristics that are the same or very similar in all three Domains. 296 Mader, Biology, 12 th Edition, Chapter 19
Grid-In Questions The following cladogram indicates similarities of certain traits between certain species. 1. According to this cladogram, how many traits do a lizard and a finch have in common? 2. What percent of organisms on this cladogram lack amniotic eggs? Mader, Biology, 12 th Edition, Chapter 19 297
The DNA alignment below shows a segment of 23 base pairs in a region common to these mammals. 3. How many nucleotides different is this segment in dogs compared to guinea pigs? 298 Mader, Biology, 12 th Edition, Chapter 19
Answers to Additional Questions for AP Practice 1. D is the correct answer. A clade includes all of the members from an ancestral group. 2. D is the correct answer. 3. Answers will vary but may include: Organisms in all three domains use energy in the form of ATP, make proteins using the code that is stored in DNA and carried by RNA, all proteins are made on ribosomes, all cells have a cell membrane. Answers to Grid-In Questions 1. Chapter: 19 Taxonomy, Systematics, and Phylogeny Answer: 5 2. Chapter: 19 Taxonomy, Systematics, and Phylogeny Answer: 37.5% (3/8)*100=37.5% 3. Chapter: 19 Taxonomy, Systematics, and Phylogeny Answer: 2 The 9 th nucleotide is an A in dogs and G in guinea pigs, and the 13 th nucleotide is a C in the dog and a G in the guinea pig. Mader, Biology, 12 th Edition, Chapter 19 299