Chapter 18 Classification and Taxonomy Linnaeus and Beyond

Chapter 18: Classification and Taxonomy Linnaeus and Beyond

Why Classify? • Biologists have identified and named about 1. 5 million species and they estimate that anywhere between 2 and 100 million additional species have yet to be discovered • To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner. • Taxonomy: discipline where scientists classify organisms and assign each organism a universally accepted name.

Assigning Scientific Names • Carl Linnaeus (1700 s) • Scientific names are assigned based on Linnaeus’ two part naming system called binomial nomenclature. Each name includes the Genus and species names. Scientific names are either written in italics or underlined. • Rules for creating a scientific name: – 1. No other species may possess the same name. – 2. The name must be derived from Latin and in some cases ancient Greek. – 3. Provide a descriptor of the organism. – 4. The name must include the genus name. • Organisms that share important characteristics are classified together and organized into groups called taxa (taxon=singular).

Linnaeus’s System of Classification • • • There are 7 taxa: Kingdom (the largest and most general group) Phylum Class Order Family Genus Species (the smallest and most specific group) The only taxon that has a clear biological identity is species. A species share a common gene pool and are actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.

Modern Evolutionary Classification • Linnaeus’s system of classification had limitations and problems. Despite being able to classify thousands of species into taxa, it did little to account for the effect of evolution. • Evolutionary classification was developed to show the common characteristics between organisms and how they developed over time. • Taxonomists today do not solely classify bases on anatomical similarities. Instead they look at evolutionary closeness and genetic similarities. Taxonomists look at nucleotide sequences of DNA and RNA on amino acid sequences of the proteins • Evolutionary classification is diagrammed in a chart called a cladogram.

A Basic Cladogram

Cladogram of Life

Cladogram Vocabulary • Taxon- Level of organization. • Roots- The dots. They represent where a trait begins. • Branchs- The lines. They represent a common thread between organisms. • Terminal Node- Where a Branch ends. • Internal Node- Where a Branch begins. • Outgroup- A group that is removed from the common root.

How to Interpret Advanced Cladograms… Time

Cladogram Type I

Cladogram Type II