State Goal Content
Evolutionary Phylogeny, DNA and Biochemical Analysis, Embryology, Morphology, Interpret Phylogenic Trees, Cladograms
Written Explanation
Evolutionary Phylogeny – Evolutionary Phylogeny is the development of a classification system that is built upon the belief that organisms descended from a common ancestor through the process of evolution. Scientists have come up with today’s classification system by many ways. Discuss what each of the following approaches is and how it contributed to creating the classification system:
Morphology – Scientists used to classify organisms strictly by morphology (what their bodies looked like), but they have learned along the way that looks aren’t everything. First, just because something can fly…doesn’t mean that it is a bird (like a bat). Or, just because something can swim, that does not mean that is a fish (a dolphin for example). So, although scientists use morphology to classify organisms today, it is not their first choice. They use other methods such as Embryology and, more preferably, DNA and Biochemical Analysis.
Embryology – Scientists have been using embryology to classify organisms for a while now. Embryology is the study of how an organism develops from an embryo (after the sperm and egg join). It has been found that the more similarly two different organisms develop as embryos, the more closely they are related in their evolutionary lineage. However, again, embryology is not the number one choice for classifying organisms today.
DNA and Biochemical Analysis – Today, scientists prefer to use DNA and Biochemical analysis to classify organisms. They feel that it is more accurate in determining the evolutionary lineage of organisms. The closer two organisms are in their evolutionary descent, the closer they should be in our classification system. Our classification system is constantly changing and DNA and Biochemical analysis is being used to reclassify many organisms at this very moment. DNA analysis is when scientists analyze the DNA of an organism and compare it to other organism. If the DNA is very similar, it is believed that the two organisms are more closely related in their evolutionary decent. If the DNA is very different, scientists believe that they are further away in their evolutionary decent. Biochemical Analysis analyzes other biochemicals in the organism, such as enzymes, proteins, chemical reactions, etc. Again, the more similarities the two organisms have, the more closely related they are considered to be.
Phylogenic Trees – Phylogenic Trees are graphic depictions of the evolutionary descent of organisms. The “branches” of the trees are separated by the different traits of the organisms as they developed over time. See the example below.
Phylogenic Trees can take many different forms. One particular form that you will be required to know how to read is called a cladogram. According to Wikipedia.org, “Cladistics is the hierarchical classification of species based on evolutionary ancestry. Cladistics is distinguished from other taxonomic classification systems because it focuses on evolution (rather than focusing on similarities between species), and because it places heavy emphasis on objective, quantitative analysis. Cladistics generates diagrams called cladograms that represent the evolutionary tree of life.” Cladograms are phylogenic trees that are very specific and the branches end with one specific species at the end of each. The 1st example below is a cladogam.
A Changing System - The current classification system is currently changing due to the discovery of new organisms as well as the discovery of new classification techniques. As long as humans strive to classify organisms, the classification of the organisms will continually change due to changes in human knowledge and technology.Linneaus with his classification system was the pioneer for the classification of organisms on earth, however, cladistics seems to be fast overriding the old system because it is based more on DNA and biochemical analysis than embryology and morphology.
Lessons and Lesson Plans
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Activities
Constructing a Cladogram
Glencoe - Cladogram and Phylogenic Tree Worksheet
Make a Cladogram Activity
"All in the Family" Cladogram Activity
Cladograms and Genetics
Constructing a Cladogram II
Cladistics is a Zip - Lab
Hardware Organisms - Lab
Hardware Organisms Supplement
Pictures & Graphics
Cladogram Example
Cladogram Example II
Animations, Movie Clips & Sounds
Classification Movie Clip
Essential Questions
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Test Items
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Formative Assessments
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Other Resources
A mnemonic for remembering the order of classification groups: http://vilenski.org/science/safari/classifyall/classify_all.html
Good pictoral of six kingdoms: http://www.ric.edu/ptiskus/Six_Kingdoms/Index.htm
The phylogenetic relationships of major groups: http://www.bookrags.com/research/phylogenetic-relationships-of-major-ansc-04/
Biography of Carl Linnaeus: http://www.ucmp.berkeley.edu/history/linnaeus.html
The Linnean System of classification: http://www.palaeos.com/Systematics/Linnean/Linnean.htm
Good tutorial on dichotomous keys with several exercises: http://www.biologyjunction.com/dichotomous_keying.htm
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