Qubi/biol200
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Objective
- To classify microorganisms and determine their relatedness using molecular sequences.
Lab Report Grading Policy
Introduction (1pt)
- Statement of objectives or aims of the experiment in the student’s own words. This is not to be copied from the Lab Manual.
Materials and Methods (0pts)
- This should be a brief synopsis and must include any changes or deviations from the procedures outlined in the Lab Manual. Specify which organisms were used to create the phylogram.
Results (4pts)
- A print out of the phylogram will suffice.
Discussion (4pts)
- Answer discussion questions.
Summary/Conclusion (1pt)
- A sentence or two will suffice
References (1pt)
- Credit is given for pertinent references obtained from sources other than the Lab Manual. This point is in addition to the 10 for the lab report.
Introduction
Evolution can be defined as descent with modification. In other words, changes in the nucleotide sequence of an organsim’s genomic DNA is inherited by the next generation. According to this, all organisms are related through descent from an ancestor that lived in the distant past. Since that time, about 4 billion years ago, life has undergone an extensive process of change as new kinds of organisms arose from other kinds existing in the past.
The evolutionary history of a group is called a phylogeny, and can be represented by a phylogram (Figure 1). A major goal of evolutionary analysis is to understand this history. We do not have direct knowledge of the path of evolution, as by definition, extinct organisms no longer exist. Therefore, phylogeny must be inferred indirectly. Originally, evolutionary analysis was based upon the organisms’ morphology and metabolism. This is the basis for the Linnaean classification scheme (the “Five Kingdoms” scheme). However, this method can lead to mistaken relationships. Different species living in the same environment may have similar morphologies in order to deal with specific environmental factors. Thus these similarities have nothing to do with how related the organisms are, but are a direct result of shared surroundings. However, with the advent of genomics, organisms can be grouped based upon their sequence relatedness. Since evolution is a process of inherited nucleotide change, analyzing DNA sequence differences allows for the reconstruction of a better phylogenetic history.
- insert image Figure 1. Tree of life based on 16S ribosomal RNA (image credit: NR Pace, Science 1997)**
Procedures
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Discussion Questions
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References
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