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MODERN CLASSIFICATION

MODERN CLASSIFICATION. Zebra Book Chapter 17 Section 2. Determining Species. Not always easy to define a species Organisms that are one species by a certain definition could be another species by a different definition As knowledge increases, definitions change

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MODERN CLASSIFICATION

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  1. MODERN CLASSIFICATION Zebra Book Chapter 17 Section 2

  2. Determining Species • Not always easy to define a species • Organisms that are one species by a certain definition could be another species by a different definition • As knowledge increases, definitions change • The concept of a species today is much different than it was 100 years ago.

  3. Typological species concept • Classification is based on comparison of physical characteristics with a type specimen • LIMITS: alleles produce a wide variety of features within a species • BENEFITS: descriptions of type specimens provide detailed records of physical characteristics of many organisms • Example… Humans

  4. Biological Species Concept • 1930s-1940s • Classification is determined by similar characteristics and the ability to interbreed and produce fertile offspring • LIMITS: some organisms, such as wolves and dogs, can interbreed and produce fertile offspring but are still separate species. Does not account for extinct species or those which reproduce asexually • BENEFITS: works in most cases, so still used frequently

  5. Phylogenetic Species Concept • Late 1940s • Companion to B.S.C. • PHYLOGENY: evolutionary history of a species • Classification is determined by evolutionary history • LIMITS: evolutionary history is not known for all species • BENEFITS: accounts for extinct species and considers molecular data

  6. CHARACTERS • Inherited features that vary among species • Used to construct patterns of descent • Morphological or Biochemical

  7. TERMS YOU NEED TO KNOW • HOMOLOGOUS: anatomically similar, functionally different • EX. Bird wing and Human Arm • ANALOGOUS: anatomically different, functionally similar • EX. Fish gill and human lung

  8. Morphological Characters • Homologous Characters: shows an anatomical similarity inherited from a common ancestor • EX. oviraptor and sparrow • What similarities do you see? http://www.critterzone.com/animal-pictures-nature/bird-sparrow-white-crowned.htm, http://mmfrankford.deviantart.com/art/Oviraptor-Philoceratops-95046955

  9. BIOCHEMICAL CHARACTERS • Use amino acids and nucleotides to determine evolutionary relationships • Also chromosome number and structure • EX. Broccoli, Cauliflower and Kale • All same Family (Cruciferae) but look completely different http://www.gardeningblog.net/how-to-grow/broccoli/, http://acozykitchen.com/parmesan-and-dill-cauliflower-puree/, http://www.treehugger.com/green-food/weekday-vegetarian-yet-another-version-kale-pesto.html

  10. Species Examples • Molecular data has changed traditional taxonomic categorization (DNA and RNA) • For example: African Savannah Elephant, African Forest Elephant and Asiatic Elephant • Asiatic Elephant is Elephasmaximusand both the African elephants are Loxodontaafricana even though the two types of African elephants have several different traits • Recent studies show that the two African elephants diverged from a common ancestor about 250 million years ago therefore scientists have considered renaming the forest elephant Loxodontacyclotis

  11. MOLECULAR CLOCK • A model that is used to compare DNA sequences from two different species to help determine how long the species have been evolving since they diverged from a common ancestor • CONVERGENT EVOLUTION: two organisms who are evolving traits which are similar • DIVERGENT EVOLUTION: two organisms from a common ancestor which develop different traits

  12. CLADISTICS • A METHOD WHICH CLASSIFIES ORGANISMS ACCORDING TO THE ORDER THAT THEY DIVERGED FROM A COMMON ANCESTOR • CLADOGRAM: A BRANCHING DIAGRAM THAT REPRESENTS THE PROPOSED PHYLOGENY OF A SPECIES OR GROUP

  13. http://en.wikipedia.org/wiki/Phylogenetic_tree

  14. TREE OF LIFE • Charles Darwin used the analogy of a tree to suggest that the majority of organisms developed from a few species • Tree Trunk represented ancestral groups, each of the branches to have similar species and the leaves were living species • This represents the diversity of living organisms • Currently there have been 1.75 million species described and more are found every year • HOW LARGE WOULD A TREE INCLUDING ALL KNOWN ORGANISMS BE???

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