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Phylogeny and Systematics

Phylogeny and Systematics. Alexander S. Berman 4A. Pages in the IB book: 448-457. Outline the value of classifying organisms. Taxonomy = the science of classification : arranging organisms into groups, which provides several advantages:

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Phylogeny and Systematics

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  1. Phylogeny and Systematics Alexander S. Berman 4A

  2. Pages in the IB book: • 448-457

  3. Outline the value of classifying organisms • Taxonomy = the science of classification: arranging organisms into groups, which provides several advantages: • species identification: members of a species share nearly all the same characteristics • predictive value: groups of related taxa share many common characteristics • evolutionary links: shared derived characteristics are inherited from common ancestors • effective communication: all scientists use the same terminology for taxonomy • Taxonomy uses both morphological and biochemical methods to distinguish homologous structures from analogous structures • avoids the problem of convergence, in which unrelated organisms have similar morphologies, called analogous structures • emphasizes homologous structures which are those derived from a common ancestor

  4. Explain the biochemical evidence provided by the universality of DNA and protein structures for the common ancestry of living organisms. • Every known living organism on earth uses DNA as its main source of genetic information • All proteins found in living organisms use the same 20 amino acids to form their polypeptide chains • Amino Acids have 2 possible orientations: left handed and right-handed. • For all living things on Earth no right amino acids were observed

  5. Explain how variations in specific molecules can indicate phylogeny • Phylogeny- study of the evolutionary past of a species • By comparing the similarities in the polypeptide sequences of certain proteins in different groups of animals one can trace their ancestery • With advances in DNA sequencing, the study of nucleic acid sequences in an organism’s DNA as well as its mitochondrial DNA has been beneficial in establishing biochemical phylogeny. • Changes in the DNA sequences of genes from one generation to another are partly due to mutations and the more differences there are between the 2 species, the less closely related the 2 species are.

  6. Discuss how biochemical variations can be used as an evolutionary clock • Differences in polypeptide sequences accumulate steadily and gradually over time as mutations occur from generation to generation in a species • By comparing homologous molecules from 2 related species. • Look at the differences between the species • Ie: 3 different species- A, B, C. Comparing DNA sequencing between the 3. Between A and B there are 23 differences. Between A and C there are 123 differences. Therefore, it can be concluded that Species A and B are closer than A and C. (Add a little TOK in there for ya)

  7. Discuss how biochemical variations can be used as an evolutionary clock • A way to measure differences: DNA Hybridization • Take 1 strand of DNA from species A and a homolgous strand from species B and fuse them together. Where the base pairs connect, there is a match; where they are repelled and do not connect, there is a difference in the DNA sequence and in conclusion no match.

  8. Define clade and cladistics • Cladistics • A system of classification which groups taxa together according to the characteristics which have most recently evolved. • Clade • a taxonomic group of organisms classified together on the basis ofhomologous features traced to a  common ancestor.

  9. Distinguish, with examples, between analogous and homologous characteristics

  10. Outline the methods used to construct cladograms and the conclusions that can be drawn from them • Make a list of organisms which will be included • List as many possible characteristics which each organism possesses • ie: backbone, hair, opposable thumbs etc • Once list has been made there will be one which is common to all of the organisms being studied • The ancestral trait is called primitive characteristics • Ie: eukaryotic, multicellular, even backbone • Make a table that shows the derived characteristics along the top row and the names of the organism in the first column • From info presented on the table you can make the cladogram • First branch from the bottom belonging to the organism with the fest derived traits. The organims with the most derived characteristics goes to the top of the last branch.

  11. Construct a simple cladogram

  12. Analyze cladograms in terms of phylogenetic relationships 1: all organisms come from a eukaryotic ancestor because based on the table (which wasn’t shown) it is obvious that they are all multi-cellular 2: the cladogram shows that lizards evolved after salamanders because they possess the derived characteristics of claws or nails, which is more evolved than the salamander’s characteristics 3: the observer can deduce from the cladogram on our left that any 2 organisms found on successive branches are more closely related to each other than those found on branches which are separated by one or more nodes ie: chimps are more closely related to mice then they are to perch. Note: see the Jaws line that was drawn? well, everything to the right of that line has jaws while everything to the left doesn’t. it was put in there to show evolution.

  13. Discuss the relationship between cladograms and the classification of living organisms • Cladograms are simply hypothesis that are drawn. • New evidence can be added which will “update” the hypothesis

  14. Bibliography • http://www.google.com/imgres?imgurl=http://www.emc.maricopa.edu/faculty/farabee/biobk/cladogram_1.gif&imgrefurl=http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookdivers_class.html&h=377&w=560&sz=26&tbnid=cBUjNOOAnlUv9M:&tbnh=73&tbnw=109&prev=/search%3Fq%3Dcladogram%26tbm%3Disch%26tbo%3Du&zoom=1&q=cladogram&docid=sK9-KkZ9M8u6MM&hl=en&sa=X&ei=3OMMT4WmPILY0QH-4djpBQ&sqi=2&ved=0CEgQ9QEwBQ&dur=199 • http://www.google.com/imgres?q=cladogram+examples&um=1&hl=en&sa=N&fhp=1&biw=944&bih=927&tbm=isch&tbnid=hcbnAV661qPr3M:&imgrefurl=http://images.yourdictionary.com/cladogram&docid=9Y4fHODBdy98fM&imgurl=http://images.yourdictionary.com/images/science/AScladog.jpg&w=456&h=316&ei=KeMMT8n_GqPv0gHclKn2BQ&zoom=1&iact=hc&vpx=283&vpy=445&dur=6467&hovh=187&hovw=270&tx=196&ty=103&sig=110955390170789937592&page=1&tbnh=127&tbnw=183&start=0&ndsp=20&ved=1t:429,r:9,s:0 • Higher level Biology book, pages 448-457

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