Systematics

• Systematics: branch of biology that studies diversity of life and is involved in reconstructing phylogenetic history
• classification of organisms into increasingly general categories: species, genus, family. order, class, phylum, kingdom
• classification schemes and phylogenetic trees are hypotheses of past history based on available data
• homology- greater number of homologous parts between two species , more closely related species are, but convergent evolution can result in analogous structures that resemble one another but have different origin (i.e. are not due to a common ancestor) e.g. wings of birds and of insects
• molecular biology- species that are phylogenetically closely related have more similar nucleotide sequences (and amino acid sequences of proteins) than do distantly related species
• mitochondrial DNA- changes by mutation faster than nuclear genome, can be used to sort out relationships between closely related species
• ribosomal RNA- DNA coding for ribosomal RNA changes slowly relative to other DNA, can be used to trace some of earliest branching in the phylogenetic tree
• molecular clocks- proteins or nucleotide sequences that have a constant rate of change over time, can calibrate in actual time by graphing number of amino acid differences or nucleotide differences vs. time (known from the fossil record), graphs can then be used to estimate the time of divergence for species, phyla, etc.

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