Classification

Why Classify? To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner. In taxonomy, scientists classify organisms and assign each organism a universally accepted name. By using a scientific name, biologists can be certain that everyone is discussing the same organism.

Aristotle 384 BC Classified organisms as either plants or animals

Carolus Linnaeus 1707-1778 Classification system Based on physical structure Taxonomic groups of related organisms Binomial nomenclature (two names ex.Homo sapiens)

Binomial Nomenclature  Carolus Linnaeus In binomial nomenclature, each species is assigned a two-part scientific name. The scientific name is always written in italics or underlined. The first word (the genus) is capitalized The second word (the species) is lowercased. EX- Genus species or Genus species Humans- Homo sapien

Linnaeus's System of Classification A group or level of organization is called a taxonomic category, or taxon Linnaeus had 7- Kingdom “King Phylum Phillip Class Came Order Over Family For Genus Great Species Spaghetti”

Taxonomic Groups

Classification of Man Kingdom Animalia Phylum Chordata Class Mammalia Order Primates Family Hominidae Genus Homo Species Homo sapiens

Species “Species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups.” Reproductively isolated group Ernst Mayr

Different Species

Checkpoint Questions: 1.  How are living things organized for study? 2. Describe the system for naming species that Linnaeus developed. 3. What are the seven taxonomic categories of Linnaeus’s classification system? 4. Why do scientists avoid using common names when discussing organisms? 5.  What is significant about members of the same species?

Modern Evolutionary Classification Organisms are grouped into categories that represent lines of evolutionary descent, not just physical similarities Modern classification systems are based upon biochemical and genetic evidence that indicates evolutionary relationships

Classification Using Cladograms Cladistic analysis identifies and considers only the characteristics that arise as lineages evolve over time. Characteristics that appear in recent parts of a lineage but not in its older members are called derived characters. Derived characters can be used to construct a cladogram, a diagram that shows the evolutionary relationships among a group of organisms.

Cladogram Evolutionary relationship of a group of organisms Each clad (group) share something in common Ancestral traits are the oldest Derived traits evolved later

Cladogram for Transportation Wheels are the most ancestral Wings are the most derived

Construct a Cladogram

Gorilla Four limbs Fur Lost tail

Tiger Four limbs Fur Tail

Lizard Four limbs Tail

Fish Tail

Chimpanzee Four limbs Fur Lost tail

Clad With 4 Limbs

Clad With Fur

Clad With No Tail

Characteristics for Constructing Cladogram Tail is the most ancestral Four limbs is the oldest derived trait Fur is a later derived trait Loss of tail is the most derived trait

Gorilla Chimpanzee Tiger Lizard Fish Tail Lost Fur Four Limbs

Gorilla Tail? How do we know the gorilla lost its tail?

Gorilla’s Vestigial Tail Human Gorilla

Traditional Classification Versus Cladogram TRADITIONAL CLASSIFICATION Section 18-2 Appendages Conical Shells Crustaceans Gastropod Crab Barnacle Limpet Crab Barnacle Limpet Molted exoskeleton Segmentation Tiny free-swimming larva TRADITIONAL CLASSIFICATION CLADOGRAM Go to Section:

Modern Evolutionary Classification Similarities in DNA and RNA The genes of many organisms show important similarities at the molecular level that can be used as criteria to help determine classification.

Modern Evolutionary Classification Comparison reveals more DNA in common, the more recent the common ancestor Molecular Clocks A model known as a molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently.

Terminology Classification Taxonomy Systematics Phylogeny Assigning organisms to different catagories based on their relationship Taxonomy The science of naming organisms Systematics Determining evolutionary relationships of organisms Phylogeny Evolutionary history

Phylogenetic Tree Shows evolutionary relationships More historical than cladogram

Echinodermata Uniramia Chelicerata Chordata Crustacea Protochordates Lophophorates Crustacea Protochordates Arthropoda Annelida Hemichordata Mollusca Other pseudocoelomates Nemertea Platyhelminthes Nematoda Ctenophora Cnidaria Mesozoa Placozoa Sarcomastigophora Ciliophora Porifera Apicomplexa Microspora Myxozoa

Birds Mammals Reptile Amphibian Fish Four Limbs Amniotic Egg Endothermic Fur Feathers Vertebrae

Monophyletic A group of all the descendants of a common ancestor The common ancestor is in the group Example: Mammalia Ancestor was a mammal like reptile

Paraphyletic A group of descendants of a common ancestor Common ancestor is in the group Not all descendants are included Example: Reptiles Does not include birds and mammals

Polyphyletic A group that has some similarities Common ancestor is in not in the group Not all descendants are included Example: Flying vertebrates

* * Archaea

Checkpoint Questions: How is information about evolutionary relationships useful in classification? How are genes used to help scientists classify organisms? 3. What is the principle behind cladistic analysis? 4. Describe the relationship between evolutionary time and the similarity of genes in two species. 5. How have new discoveries in molecular biology affected the way in which we classify organisms compared with the system used by Linnaeus?