Jan 22 Phylogeny Lab Part 1.pdf

Jan 22 Phylogeny Lab Part 1.pdf - Phylogenetics Lab Since...

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Phylogenetics Lab Since the time of Darwin, biologists have be interested in classifying and organizing the vast amounts of diversity among living organisms. Systematics is the study of biological diversity and evolutionary relationships between groups of organisms. It is made up of two fields: Taxonomy and Phylogenetics . Taxonomy is the classification of organisms into groups. Phylogenetics is the reconstruction of evolutionary relationships between these groups. What is a phylogeny? A phylogeny is the graphical representation of the hypothesized evolutionary relationship between taxa. These trees represent the best hypothesis of evolutionary relationships given the data available. There is no way to truly know how species or groups of organisms are related as we were not present to observe these changes. We are forced to compile evidence of shared ancestry to create possible scenarios (phylogenetic trees) of how groups may be related. The more data we use, the better informed the possible trees. However, different sets of data can often tell different stories. It is the goal of phylogeneticists to compile the best data and compare all possible trees to determine the most likely story of the organism’s evolutionary history. What types of data are used to build phylogenetic trees? Traits used as phylogenetic characters (data used to build phylogenetic trees) must be homologous (i.e. similar because they came from a common ancestor). They must have a genetic basis, be independent, and reflect the organism’s phylogeny. Early on, morphological traits were most commonly used because they are inexpensive to characterize, they can be observed in the fossil record, and allow for the characterization of many individuals. However, the genetic basis for many morphological traits is not fully understood and there is variation in morphological traits that may not be phylogenetically informative. More recently, molecular data has been the character of choice for phylogenetic studies. Each DNA base pair can be used as a phylogenetic character, allowing for access to large amounts of genetically based data that can be used to inform phylogenetic trees.
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