Taxonomy and Systematics PDF

General Biology 2 Lesson 4 Basic Taxonomic Concepts Presented by Joan A. Riparip SEATWORK My Family Tree  Learning Objectives At the end of the lesson, you should be able to: Explain how the structural and developmental characteristics and relatedness of DNA sequences...

General Biology 2 Lesson 4 Basic Taxonomic Concepts Presented by Joan A. Riparip SEATWORK My Family Tree  Learning Objectives At the end of the lesson, you should be able to: Explain how the structural and developmental characteristics and relatedness of DNA sequences are used in classifying living things Identify the unique/ distinctive characteristics of a specific taxon relative to other taxa Describe species diversity and cladistics, including the types of evidence and procedures that can be used to establish evolutionary relationships.  INTRODUCTION Truly overwhelming is the variety of living species on earth. Throughout human history, people have come up with ways of organizing, or classifying biological diversity. Organisms, including general similarities, colors, ecological functions, etc. The most effective way for scientists to organize biological diversity is according to shared evolutionary background that leads to organized classification, and transmits knowledge about understanding evolutionary past. Taxonomy vs. Systematics Systematics is the study of the diversification of life forms over time, both past and present, and their relationships between other species. On the other hand, taxonomy is the science of organizing and categorizing living organisms into classes called taxa. Taxonomy vs. Systematics Both a systematist and a taxonomist provide scientific names; give detailed descriptions of organisms; collects and keeps volumes of specimens; offer classifications for the organisms by constructing identification keys and data on their occurrence and distribution. However, it is the systematist that investigates on evolutionary histories and considers environmental adaptation of species. A. Linnaean System of Classification Linnaeus was a Swedish botanist who lived during the 1700s. He is known as the “father of taxonomy.” Linnaeus tried to describe and classify the entire known natural world. In 1735, he published his classification system in a work called Systema Naturae (“System of Carolus Linnaeus Nature”). classification system has seven levels. Each level is included in the level. Levels get increasingly specific from kingdom to species.  seven levels. Kingdom - This is the highest taxon in Linnaean taxonomy, representing major divisions of organisms. Kingdoms of organisms include the plant and animal kingdoms. Phylum (plural, phyla) - This taxon is a division of a kingdom. Phyla in the animal kingdom include chordates (animals with an internal skeleton) and arthropods (animals with an external skeleton).  seven levels. Class - This taxon is a division of a phylum. Classes in the chordate phylum include mammals and birds. Order - This taxon is a division of a class. Orders in the mammal class include rodents and primates. Family - This taxon is a division of an order. Families in the primate order include hominids (apes and humans) and hylobatids (gibbons).  seven levels. Genus - This taxon is a division of a family. Genera in the hominid family include Homo (humans) and Pan (chimpanzees). Species - This taxon is below the genus and the lowest taxon in Linnaeus’ system. Species in the Pan genus include Pan troglodytes(common chimpanzees) and Pan paniscus (pygmy chimpanzees system has seven levels. system has seven levels. Binomial nomenclature is a two-part scientific naming system. Uses Latin words Scientific names always written in italics Two parts are the genus name and species descriptor Homo sapiens Common name: humans  Binomial nomenclature A genus includes one or more physically similar species. Species in the same genus are thought to be closely related. Genus name is always capitalized. A species descriptor is the second part of a scientific name. always lowercase always follows genus name; never written alone  Binomial nomenclature Scientific names help scientists to clearly communicate about species. Some species have very similar common names. Some species have many common names. Why have a classification system? 01 Single, universal name Avoid confusion 02 Understand 03 another how living things are related to one The Linnaean classification system has limitations. Linnaeus taxonomy doesn’t account for molecular evidence such as DNA sequencing. The technology didn’t exist during Linnaeus’ time. Linnaean system based only on physical similarities. Physical similarities are not always the result of close relationships. Genetic similarities more accurately show evolutionary relationships. Three Domain System  Levels of Classification Scientists split species into three large groups after the usual beginning of all life. Bacteria, Archaea, and Eukarya are groups called domains. After domains, the following categories of increasing specificity are kingdoms: phylum, class, order, family, genus, and species.  Classification System How are organisms classified TODAY? All living organisms are classified into one of three domains BACTERIA ARCHAEA EUKARYA  Bacteria These organisms have 3 basic characteristics They are unicellular They are prokaryotic They live everywhere around us  Archaea These organisms have 3 basic characteristics They are unicellular They are prokaryotic They live in Earth’s most extreme environments  Archaea These environments are too extreme for any other organisms on Earth because they’re: Too hot Too acidic or alkaline So how are bacteria and archaea similar but different?  Eukarya Organisms in this domain have only 1 in common They are eukaryotes Eukarya There are 4 types of eukaryotic organisms (also known as kingdoms) Protists Fungi Plants Animals  Protists These organisms have 3 basic characteristics They heterothrops They can be classified as plants animals or fungi Seaweed Amoeba Slime mold  Fungi These organisms have 3 basic characteristics They heterotrops Most of them feed from dead organisms They are multicellular Only few fungi species are unicellular They are eukaryotes Mushroom Molds Mildew  Plants These organisms have 3 basic characteristics They are autotrophs They produce their own food through photosynthesis They are multicellular They are eukaryotes Plants Moss Trees  Animals These organisms have 3 basic characteristics They are heterotrophs They are multicellular They are eukaryotes They move Sea stars insects Vertebrates  So now you know it! DOMAIN Kingdoms Figure: Levels in taxonomic classification: At each sublevel in the taxonomic classification system, organisms become more similar. Dogs and wolves are the same species because they can breed and produce viable offspring, but they are different enough to be classified as different subspecies. The following table shows four species that are classified using the Linnaean system of classification. Features are used as bases for classification. The following table shows four species that are classified using the Linnaean system of classification. Features are used as bases for classification.  B. Classification Based on Evolutionary Relationships KEY CONCEPT Modern classification is based on evolutionary relationships. Phylogeny Cladistics  Phylogeny Phylogeny is the study of relationships and their evolutionary development among different groups of organisms. A phylogeny is commonly represented by a phylogenetic tree called a tree diagram. An early example of a phylogenetic tree is the "Tree of Life" by Darwin Phylogeny is the evolutionary history for a group of species. Evidence from living species, fossil record, and molecular data is used The "Tree of Life" by Darwin The Phylogenetic Tree Figure 2. The root of a phylogenetic tree indicates that an ancestral lineage gave rise to all organisms on the tree. A branch point indicates where two lineages diverged. A lineage that evolved early and remains unbranched is a basal taxon. When two lineages stem from the same branch point, they are sister taxa. A branch with more than two lineages is a polytomy. Building Phylogenetic trees How do scientists construct phylogenetic trees? After the homologous and analogous traits are sorted, scientists often organize the homologous traits using a system called cladistics. This system sorts organisms into clades: groups of organisms that descended from a single ancestor.  Cladistics Cladistics is classification based on common ancestry. Cladistics is a common method to make evolutionary trees. Species placed in order that they descended from common ancestor.  Cladistics A cladogram is an evolutionary tree made using cladistics. Derived characters are traits shared in different degrees by clade members. The basis of arranging species in cladogram more closely related species share more derived characters represented on cladogram as hash marks  Cladistics Nodes represent the most recent common ancestor of a clade. Clades can be identified by snipping a branch under a node. NODE Cladistics  Shared Characteristics Organisms evolve from common ancestors and then diversify. Scientists use the phrase “descent with modification” because even though related organisms have many of the same characteristics and genetic codes, changes occur. This pattern repeats over and over as one goes through the phylogenetic tree of life: 1. A change in the genetic makeup of an organism leads to a new trait which becomes prevalent in the group. 2. Many organisms descend from this point and have this trait. 3. New variations continue to arise: some are adaptive and persist, leading to new traits. 4. With new traits, a new branch point is determined (go back to step 1 and repeat).  Shared Characteristics If a characteristic is found in the ancestor of a group, it is considered a shared ancestral character because all of the organisms in the taxon or clade have that trait. The vertebrate is a shared ancestral character. Now consider the amniotic egg characteristic in the same figure. Only some of the organisms have this trait, and to those that do, it is called a shared derived character because this trait derived at some point but does not include all of the ancestors in the tree.  Choosing the Right Relationships Organizing the evolutionary relationships of all life on Earth proves much more difficult: scientists must span enormous blocks of time and work with information from long-extinct organisms To aid in the tremendous task of describing phylogenies accurately, scientists often use a concept called maximum parsimony, which means that events occurred in the simplest, most obvious way. For example, if a group of people entered a forest preserve to go hiking, based on the principle of maximum parsimony, one could predict that most of the people would hike on established trails rather than forge new ones.  Limitations of Phylogenetic Trees Closely-related species may not always look more alike, while groups that are not closely related yet evolved under similar conditions, may appear more similar to each other. In phylogenetic trees, branches do not usually account for length of time and only depict evolutionary order. Phylogenetic trees are like real trees in that they do not simply grow in only one direction after a new branch forms; the evolution of one organism does not necessarily signify the evolutionary end of another. Limitations of Phylogenetic Trees  Summary To build phylogenetic trees, scientists must collect accurate information that allows them to make evolutionary connections between organisms. Using morphologic and molecular data, scientists work to identify homologous characteristics and genes. Similarities between organisms can stem either from shared evolutionary history (homologies) or from separate evolutionary paths (analogies). Newer technologies can be used to help distinguish homologies from analogies. After homologous information is identified, scientists use cladistics to organize these events as a means to determine an evolutionary timeline. Scientists apply the concept of maximum parsimony, which states that the order of events probably occurred in the most obvious and simple way with the least amount of steps. For evolutionary events, this would be the path with the least number of major divergences that correlate with the evidence. Thank you! Do you have any questions? www.reallygreatsite.com