MODERN CLASSIFICATION
Zebra BookChapter 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• The concept of a species today is much different than it was 100 years ago.
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
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
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
CHARACTERS• Inherited features that vary among species•Used to construct patterns of descent•Morphological or Biochemical
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
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
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
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 Elephas maximus and both the African elephants are Loxodonta africana 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 Loxodonta cyclotis
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
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
http://en.wikipedia.org/wiki/Phylogenetic_tree
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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