1. Classification
Chapter 18

2. What is Classification?
Classification is used to name organisms as well as group them in a logical manner.
Taxonomy is the classification and naming of organisms.
Why are scientific names important? It helps make sure that scientists are talking about the same organism. If we just used the name bird we wouldn’t know exactly what bird we are talking about.

3. Scientific Naming
Common names can be confusing because they can be different in different languages or regions.
Example: buzzard – in the UK it means hawks, in the US it means vulture.
Latin and Greek are used in scientific naming.
Binomial nomenclature – this is the current scientific naming system that gives each species two-part scientific name.
The scientific name is always italicized and the first word capitalized and the second lowercase.

4. Example of scientific naming: a grizzly bear is Ursus arctos
Example of scientific naming: a grizzly bear is Ursus arctos. The first word is Ursus which is the genus the organism belongs to.
Genus – is a group of closely related species. The genus Ursus includes grizzly bears, polar bears, black bears, and brown bears.
The second part of a scientific name is unique to each species. It is usually a description of the organism. For polar bears, Ursus maritimus, maritimus refers to the sea – where polar bears are found.

5. Linnaeus’s System of Classification
Linnaeus’s System had 7 levels: (smallest to largest) species, genus, family, order, class, phylum, and kingdom.
These levels are called taxon (taxonomic category).
A family is a group of genera that are related. The bear belongs to the family Ursidae.
An order is made of similar families. The bear belongs with dogs, cats, and other animals in the order Carnivora.
Class is made of similar orders. The bear is in class Mammalia. These are animals that are warm- blooded, have body hair, and produce milk for their young.
Several class will make up a phylum. Mammals, birds, reptiles, amphibians, and fish are all in the phylum Chordata. They have similar body plans and internal functions.
Lastly, kingdom is the largest category. Bears are in the kingdom Animalia.
Linnaeus only had 2 kingdoms: animmalia and plantae

7. Modern Evolutionary Classification
With Darwin’s ideas about evolution (descent with modification) this has given rise to the study of phylogeny, or evolutionary relationships, not just physical similarities.
This is called evolutionary classification.
Species in a genus will be more closely related to one another than species in another genus. All members of a genus will share a common ancestor.

8. Classification Using Cladograms
Cladistic analysis identifies and considers characteristics of an organism that are evolutionary – new characteristics that have evolved over time. These characteristics are called derived characters.
Theses characteristics are used to make a cladogram. This shows evolutionary relationships. (we will talk about this in class).

9. Similarities in DNA or RNA
DNA and RNA can be used to compare different organisms because they are used by every organism.
The genes of many organisms can show similarities at the molecular level (DNA level). This can be used to classify and determine evolutionary relationships.
Organisms that look very different can have some similar genes. For example, humans and yeast both have genes for myosin. This may indicate they shared a common ancestor.
The more similar 2 species are the more closely related they are, the more similar their DNA is.

10. Molecular Clocks
A molecular clock uses DNA comparisons to estimate the length of time that 2 species have been evolving independently.
Comparing DNA to how dissimilar genes are tells us how long ago the 2 species shared a common ancestor.