KEY CONCEPT Modern classification is based on evolutionary relationships.

Physical similarities are not always the result of close relationships. Genetic similarities more accurately show evolutionary relationships.

PHYLOGENY Biologists group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. Phylogeny = the study of evolutionary relationships among organisms.

Phylogenetic Tree

Phylogenetic trees are usually based on a combination of these lines of evidence:     Fossil record     Morphology (structure)     Embryological patterns of development     Chromosomes and DNA

PHYLOGENY Classification using Cladograms Cladograms are diagrams that show the evolutionary relationships among a group of organisms. A phylogenetic tree is a specific type of cladogram where the branch lengths are proportional to the predicted or hypothetical evolutionary time between organisms or sequences. Cladograms are branched diagrams, similar in appearance to family trees, that illustrate patterns of relatedness where the branch lengths are not necessarily proportional to the evolutionary time between related organisms or sequences.

PHYLOGENY Example of a cladogram A B C D E F Speciation: formation of two new species from one Clade or lineage TIME Definition of Clade: A group of organisms, such as a species, whose members share homologous features derived from a common ancestor. The American Heritage® Dictionary of the English Language, Third Edition copyright © 1992 by Houghton Mifflin Company. Electronic version licensed from INSO Corporation; further reproduction and distribution restricted in accordance with the Copyright Law of the United States. All rights reserved.

CLADOGRAMS This cladogram shows the evolutionary relationship among several vertebrates. Fur & Mammary Glands Jaws Lungs Claws or Nails Feathers Hagfish Fish Frog Lizard Pigeon Mouse Chimp

CLADOGRAM Fur & Mammary Glands Jaws Lungs Claws or Nails Feathers Hagfish Fish Frog Lizard Pigeon Mouse Chimp Characteristics listed below the line are called derived characters (traits).

CLADOGRAM Fur & Mammary Glands Jaws Lungs Claws or Nails Feathers Hagfish Fish Frog Lizard Pigeon Mouse Chimp Do frogs have mammary glands? Do hagfish have jaws? When the derived character is above an organism, the organism lacks that derived character.

3. CLADOGRAM Fur & Mammary Glands Jaws Lungs Claws or Nails Feathers Hagfish Fish Frog Lizard Pigeon Mouse Chimp Do pigeons have claws or nails? Do lizards have jaws? When the derived character is below the organism, the organism possesses that derived character.

copyright cmassengale Primate Cladogram copyright cmassengale

The Dichotomous Key Device for easily and quickly identifying an unknown organism. The dichotomous key is the most widely used type in biological sciences. The user is presented with a sequence of choices between two statements, couplets, based on characteristics of the organism. By always making the correct choice, the name of the organism will be revealed.

copyright cmassengale Dichotomous Keying Used to identify organisms Characteristics given in pairs Read both characteristics and either go to another set of characteristics OR identify the organism copyright cmassengale

Example of Dichotomous Key 1a Tentacles present – Go to 2 1b Tentacles absent – Go to 3 2a Eight Tentacles – Octopus 2b More than 8 tentacles – 3 3a Tentacles hang down – go to 4 3b Tentacles upright–Sea Anemone 4a Balloon-shaped body–Jellyfish 4b Body NOT balloon-shaped - 5 copyright cmassengale

  A. one pair of wings B. Two pairs of wings