Eucarya: A eukaryote is an organism with a complex cell or cells, in which the genetic material is organized into a membrane-bound nucleus or nuclei.

Enzyme: A class of proteins that are capable of catalyzing chemical reactions (the making or breaking of chemical bonds). They do so by orienting their substrates into a suitable geometry in a particular location (the active site) where electrophilic or nucleophilic amino acid residues can participate in the reaction. Enzymes are protein catalyst that speeds up chemical reactions that would otherwise be prohibitively slow under physiological conditions.

Eukaryote: A cell or organism with a distinct membrane-bound nucleus as well as specialized membrane-based organelles (see also prokaryote).

Exon: The region of DNA within a gene that codes for a polypeptide chain or domain. Typically a mature protein is composed of several domains coded by different exons within a single gene.

E-value: For a given score, the number of hits in a database search that we expect to see by chance with this score or better.

Endonuclease: An enzyme that cleaves phosphodiester bonds at internal sites in a nucleic acid molecule.

Entrez: An online retrieval system for searching several linked databases, provided by the National Center for Biotechnology Information (NCBI).

Evolution: A process operating on populations that involves variation among individuals, traits being inheritable, and a level of fitness for individuals that is a function of the possessed traits.

Evolutionary tree: A diagram showing the evolutionary history of organisms based on differences in amino acid sequences.