Why Classify?

 Organization is necessary when dealing with large numbers of something  It’s easier to work if there is a system of how to keep track of things  If you have a specific place for something, then you don’t spend time hunting around trying to find it  There are some million organisms on Earth!  Biologists organize according to similarities and proposed relationships Tacitus bellus

A common name can be used by more than one species A scientific name must be unique Erithacus rubicula Robin Turdus migratorius Robin

A group of organisms that can reproduce only among themselves and that are usually contained in a geographic region Asian Elephant Elephas maximus African Elephant Loxodonta africana

Taxonomy, the ordered division of organisms into categories based on similarities and differences Systematic Taxonomy, commonly called systematics, is the study of the evolution of biological diversity. Populus tremuloides Quaking Aspen

 Phylogeny is the evolutionary history of a species or group of related species › classifies organisms and their evolutionary relationships using  fossils  morphology  embryology  molecular evidence Black Swan nesting Cygnus atratus

 Planet Earth is about 4.6 billion years old.  Oldest known rocks are about 3.8 billion years old.  Oldest fossils (prokaryotes) are about 3.5 billion years old.

 All living organisms on this planet share a common ancestor.  What is the evidence?  The tree of life reflects the branching pattern of speciation  A phylogenetic history of life that has occurred since the origin of life.

Swedish biologist considered the father of modern taxonomy. binomial nomenclature hierarchical classificationScience of Systematics dates to Linnaeus in the 18 th century who devised the basic systems of binomial nomenclature and hierarchical classification All organisms have a unique binomial name Humans are Homo sapiens

 The arrangement of organisms in a series of nested groups, in which similar or related groups at one level are combined into larger and more general groups at the next higher level.  Biological classification is based on shared descent from the nearest common ancestor

Each categorization at any level is called a taxon.

characters  Phylogenetic trees are constructed by studying features of organisms formally called characters.  Characters may be morphological or molecular. homology  Character similarity resulting from shared ancestry is called homology.

 In a phylogenetic tree the tips of the branches specify particular species and the branching points represent common ancestors.

 The aim is to figure out the evolutionary relationships among species.  Branching diagrams called phylogenetic trees hypothesize evolutionary relationships thought to exist among groups of organisms.  Why a hypothesis?

 Cladograms are also diagrams that display patterns of shared characteristics.  Within a tree a clade is defined as a group that includes an ancestral species and all of its descendants.  Cladistics is the science of how species may be grouped into clades.

 A cladogram and a phylogenetic tree are similar, but not identical.  Traditional evolutionary taxonomy is subjective and therefore more prone to bias. A phylogenetic tree’s branches put more emphasis on certain characters rather than others.. It is thought that evolutionary success is dependent on high-impact events.  Cladistics treats each character equally. It is more objective by ignoring how some characters have a higher impact on evolution

MammalsTurtlesLizards and Snakes CrocodilesBirdsMammalsTurtlesLizards and Snakes CrocodilesBirds CladogramPhylogenetic Tree  What’s the difference? CLADISTICSPHYLOGENY  Essentially CLADISTICS and PHYLOGENY are the same

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

 The fossil record refers to the order in which fossils appear within layers of rock that mark the passing of geologic time.

 Comparing physical structural characteristics

Similarities due to shared ancestry

adaptations These animals have evolved similar adaptations because they occupy similar environments. Convergent Evolution and Analogous Structures

Convergent Evolution Convergent Evolution Similar solutions to similar problems Analogous Structures Traits that are morphologically and functionally similar even though there is no common ancestor.

Chromosomes and DNA

 An organism’s evolutionary history is documented in its genome  The rate of evolution of DNA sequences varies from one part of the genome to another  Comparing the different sequences helps us to investigate relationships between groups of organisms that diverged long ago  DNA that codes for ribosomal RNA and mitochondrial DNA are both used

 Amount of genetic difference between sequences is a function of time since separation.  Rate of molecular change is constant (enough) to predict times of divergence

 The more alike the DNA sequences of two organisms, the more closely related they are evolutionarily.  Early phylogenetic tree of amniotes based on cytochrome c gene by Fitch and Margoliash (1967).  Note numbers on branches.  These represent estimated numbers of mutational changes in gene.

 Ancestral:  Trait of the ancestor  Derived:  Trait that is present in the organism, but not in the common ancestor of the group

 A dichotomous key is a written set of choices that leads to the name of an organism.  "Dichotomous" means "divided into two parts". Therefore, dichotomous keys always give two choices in each step.  After each description, the key directs the user to another pair of descriptions or identifies the organism. Example: 1 a) Is the leaf simple? Go to 2 b) Is the leaf compound? Go to 3 2.a) Are margins of the leaf jagged? Go to 4 b) Are margins of the leaf smooth? Go to 5 A bee Osmia ribifloris on a barberry flower

 When the authors of your text book were in high school they were taught two kingdoms: plants and animals.  When your teacher was in high school she was taught five kingdoms: Monera, Protista, Plantae, Fungi and Animalia

 Now biologists have adopted a three- domain system › Discovery that there are two distinct lineages of prokaryotes CharacteristicBacteriaArchaeaEukarya Nuclear envelopeNo Yes Membrane-enclosed organelles No Yes IntronsNoYes Histone proteins associated with DNA NoYes Circular chromosomeYes No