Bio102 classification

ClassificationBiology 102

• Classification– The systematic arrangement in groups or categories

according to established criteria – Organizing the types of shoes in a shoe store or the

screws, bolts, and nails at a hardware store• Taxonomy

– The scientific discipline that specializes in classifying organisms and assigning them to internationally accepted groups

– Assign names to organisms using common rules• Binomial nomenclature

What’s in a name?• Prior to the creation of binomial nomenclature,

organisms were give common names that were not necessarily internationally accepted or known

• Common names led to confusion • Binomial nomenclature

– Literally translates to “two-name naming system”– Systematic method of naming an organism– Each organism given two names; written in italics (or

underlined) and the first word is always capitalized– Examples:

• Homo sapiens (abbreviated H. sapiens) – humans• Escherichia coli (abbreviated E. coli) – common

bacteria found in mammalian intestines

Linnaean Classification• Carolus Linneaus

– Father of modern taxonomy– Swedish botanist who lived in the 18th Century– Developed the classification system which bears his

name• System divides life into a series of taxa

– Taxa is the plural form of taxon– Based on observable characteristics (i.e., length of a

bone, size/shape of a flower, etc.)• Divided life into two broad groups

– Animalia – animals– Plantae - plants

Linnaean Classification• Seven Taxonomic Categories

– Begins with the Kingdom which is the largest and most inclusive category

– Concludes with the Species which is the smallest and least inclusive (or most exclusive)

– Kingdom• Phylum

– Class» Order

- Family- Genus - Species

Linnaean Classification• The binomial nomeclature system uses the genus + the

species name to refer to specific organisms – The genus + species name is also referred to as the

“specific epithet”• Additional kingdoms

– In the 20th century, 3 kingdoms were added:• Protista• Fungi• Monera

• Why do the taxa exist?– Big problem with Linnaean taxonomy is that it does not

explain why organisms with similar traits arrived at those traits

– Groups simply defined based on having (or not having) a particular characteristic

Modern Evolutionary Classification• Built on the Linnaean framework with the seven

taxonomic categories roughly intact– Modern framework diagram

• Relationships, not just physical similarity– Organisms are now grouped based on evolutionary

descent (“descent with modification” – C. Darwin)• In other words, groupings are based on genealogy

Modern Evolutionary Classification• Relationships, not just physical similarity

(continued)– Physical and genetic factors can be used to

determine relationships• Derived characters – characteristics that are only

found in recent parts of a lineage and not among the older members

– Can be physical and genetic structures– Enter The 4th Dimension

• Can use changes in the code of a gene to quantify the passage of time (molecular clock)

• This fact can be used to determine how long ago species were related

• Molecular clock diagram

Cladograms• Scientists can take the data on derived characters (both

genetic and physical) and plot them on a graph– This type of graph is called a cladogram

• Making a cladogram– Group organisms based on shared derived characters– Plot individual species or groups of species with the

same derived character together on the cladogram– Species that do not share a derived character are

plotted further away from one another– Let’s try the Quick Lab on page 453 in your textbook

• Cladograms depict the evolutionary relationship among species– If a large enough number of species are considered,

we are looking at the “Tree of Life”

The first “tree of life”Sketch from Darwin’s notebook

Darwin on the “Tree of Life”• “The affinities of all the beings of the same class have

sometimes been represented by a great tree….The green and budding twigs may represent existing species; and those produced during each year may represent the long succession of extinct species…As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.”

Modern Evolutionary Classification• Using evolutionary relationships (both from physical and

genetic evidence), we can construct evolutionary tree of life for the species currently alive on the planet– Tree of life diagram – from textbook– Tree of life diagram – not from textbook = better!

• Looking at life through the evolutionary “lens” showed us that the 5 Kingdom model needed revision

• Genetic evidence indicated larger taxa than the kingdom– Domains are super-groups that include one or more

kingdoms– The three domains are:

• Bacteria• Archaea• Eukarya

Three Domains• Domain Bacteria

– Unicellular, prokaryotes– Formerly classified as Kingdom Monera– Literally found everywhere on the planet– Some are free-living, while others require a host to

survive– Some are autotrophs, whiles others are heterotrophs

• Domain Archaea– Unicellular, prokaryotes– Formerly classified as Kingdom Monera– Once thought to be forms of ancient life (hence the

name), but now thought to be modern life adapted to extreme environments (i.e., hot springs, brine pools, hydrothermal vents)

– Some are autotrophs, while others are heterotrophs

Three Domains• Domain Eukarya

– Uni- and multicellular eukaryotes– Some are heterotrophic, while others are autotrophic– Comprised the other 4 kingdoms: Protista, Fungi,

Plantae, and Animalia• Characteristics of Life Table

Modern interpretation of Linnaean taxa

The molecular clock just keeps on ticking

The Tree of Life – from textbook

The Tree of Life – better, more representative = not from textbook