Chapter20

Ch. 20: The Classification of Organisms: 

Ch. 20: The Classification of Organisms Tiffany Liu Period 1

Species: 

Species More than 5 million different species have been grouped and named by biologists Species: the most basic unit of biological classification ( means “kind” in Latin) Practical purposes: species is a category that has certain guidelines as to an organism’s structure and appearance.

More species: 

More species 1940: Ernest Mayr of Harvard University said that species are “groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.” If members of one species exchanged genes with another species, they would no longer have special characteristics that identify them as different organisms.

Speciation: 

Speciation A group (species) of organisms are reproductively united but can change as time passes, and as they move over the Earth, Over 3.5 million years, speciation has led to the diversity of organisms.

Genera: 

Genera Groups of closely related species are genera (singular, genus). The genus is the 1st part of an organism’s scientific name: genus + epithet (adj.). This is known as a binomial. Genus and species names are given by whoever discovers it. Some name them after themselves or friends, but some name them for fun (ex. Ytu brutus, a beetle)

Taxonomy: 

Taxonomy The classification of organisms -consists of groups within groups taxon: a particular group Category: the level at which the taxon is ranked. http://www.differentphotos.com/IMAGES/E_rubecula1.jpg

Carolus Linnaeus: 

Carolus Linnaeus Three categories were in use in his time: genus, species, and kingdom. Kingdom: the highest level. He and other scientists added many levels: families, orders, classes, and phyla/ divisions. Division: used for prokaryotes, algae, fungi, and plants Phylum: used for protozoa and animals

Taxonomy continued: 

Taxonomy continued Kingdom: Plantae Division: Anthophyta Class: Dicotyledones Order: Sapindales Family: Aceraceae Genus: Acer Species: Acer rubrum English name: Red maple http://www.ridgecrestnursery.com/Trees/Maple_Trees/Red_Maple_Montgomery.jpg

Evolutionary Systematics: 

Evolutionary Systematics Phylogeny: an organism’s evolutionary history Systematics: the study of the historical relationships among organisms http://www.gov.bw/tourism/multimedia/img/leopard.jpg

Slide10: 

Monophyletic: the idea that the members of a taxon should all be descended from the nearest common ancestral species. Polyphyletic: the idea that some taxa containing organisms descended from more than one ancestral line.

Homology and Analogy: 

Homology and Analogy Structures that have a common origin but not a common function are called homologues. Ex: Arm of a human to that of a crocodile http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Taxonomy.html Structures that have a common function and appearance but not a common origin and called analogues. Ex: wing of a bird to that of an insect

Evolutionary Taxonomy: 

Evolutionary Taxonomy The organism is assigned, tentatively, to a taxon based on its outward appearance. The similarities are tested for homologies. Fossils are taken into account when possible, as well as patterns of embryonic development. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Taxonomy.html#EmbryonicDevelopment

Alternative Methods…: 

Alternative Methods… Numerical Phenetics This is based only on the characteristics that can be observed, thus homology is not taken into account. The characteristics are divided into characters that can’t be divided even more, then they are assigned numbers. The data is then processed and scores Ex: Both lizards and humans have 5 fingers, while a snake has none, so lizards and humans are more closely related.

Another Alternative Method: 

Another Alternative Method Cladistics Ignores overall similarity and is based solely on genealogy. More recent branches are assigned lower ranks. Holophyletic: a taxon that includes all of the descendants from an ancestor, as well as the ancestor. Paraphyletic: A taxon that consists of a holophyletic group from which very different members, and perhaps the ancestor even, have been removed.

Biochemical techniques…: 

Biochemical techniques… They offer two advantages The results can be counted Diverse organisms can be compared They can compare enzymes, reaction pathways, hormones, and structural molecules It is now possible to compare organisms on the level of the gene.

Amino Acid Sequences: Cytochrome c: 

Amino Acid Sequences: Cytochrome c One of the 1st proteins that was analyzed was cytochrome c. The molecule, from many organisms, was analyzed, and showed the number of amino acids that the organisms differed by. The greater the number, the more distant their evolutionary relationship. The results were similar to the phylogenies made by other methods.

Amino Acid Sequences cont’d: 

Amino Acid Sequences cont’d Some biologists believe that the differences in protein structure represent functional differences Others think that they occur at random because of random mutations and represent the passage of time. The “random- tick” hypothesis states that they can be used to determine when a particular group branched off (molecular clocks).

Nucleotide sequences: 

Nucleotide sequences Far easier since there are only 4 nucleotides vs. 20 amino acids More sensitive since changes in nucleotides do not necessarily reflect in amino acids Analyses between rRNA and tRNA of prokaryotes can begin determining relationships among them. However there are many molecular clocks, ticking at different speeds (ex. mutations and introns).

DNA-DNA Hybridization: 

DNA-DNA Hybridization One of the earliest techniques used to study nucleic acids Charles G. Sibley and Jon E. Ahlquist Produced hybrid radioactive DNA, then reheated it to determine similarity: the higher the temperature at which it broke apart, the more similar the DNA. 50% dissociation temp. is a base line: a 1 degree C change equals a 1% difference in the nucleotide sequences which equals a 4.5 million year evolutionary separation.

DNA-DNA Hybridization cont’d: 

DNA-DNA Hybridization cont’d Mitochondrial DNA evolved faster than nuclear DNA Answers questions about relationships of organisms Helped prove the giant panda is a bear, not a raccoon. Helps ask more questions about evolutionary relationships. http://leisure.mytrip.net/shirahama/img/map/panda.jpg

Kingdoms Before…: 

Kingdoms Before… The placement of taxa within kingdoms remains an unsolved problem In Linnaeus’s time there were only three kingdoms: animals, plants, and minerals Fungi, algae, and bacteria were grouped with plants Protozoa were grouped with animals

Kingdoms are Modified…: 

Kingdoms are Modified… 20th century: bacteria are placed in separated kingdom due to new evidence Resulted from improvements in microscopes and biochemical techniques. More evidence on evolutionary systems Eukaryotes arose from prokaryotes Multicellular organisms from unicellular organisms.

Kingdoms After…: 

Kingdoms After… Monera Based on cellular organization and biochemistry Protista Eukaryotes autotrophic and heterotrophic Unicellular and multicellular Fungi Absorb nutrients from their environment Plantae Photosynthesize their organic molecules Animalia Eat other organisms