The largest unit in the current taxonomic nomenclature. Members of the three domains (Bacteria, Archaea, and Eukarya) are believed to have been evolving independently of each other for at least a billion years. Dominance • In genetic terminology, the ability of one allelic form of a gene to determine the phenotype of a heterozygous individual, in which the homologous chromosome carries both it and a different allele. For example, if and are two allelic forms of a gene, is said to be dominant to if AA diploids and Aa diploids are phenotypically identical and are distinguishable from aa diploids. The allele is said to be recessive.

a category ranked above kingdom in taxonomy; archaea and bacteria are considered by most to be distinct domains, after once being thought to be in the same kingdom (Archaebacteria); archaea were distinguished from other prokaryotes (Eubacteria) before the distinction between these groups of prokaryotes was shown to be more fundamental.

The highest level of biological classification, superseding kingdoms. The three domains of biological organisms are the Bacteria, the Archaea, and the Eukarya. Also used to describe a region of a protein having a distinct function.

Broadest level of scientific classification; above Kingdom

a category larger than a kingdom. Three domains make up the Tree of Life: Archaea, Bacteria, and Eukarya. Each contains many kingdoms.

The highest taxonomic division in the classification of living organisms. The three domains are the Archaea, the Bacteria and the Eucarya. Domains are subdivided into kingdoms. While the three domain model is widely used in astrobiology, some biologists prefer other schemes such as the Five Kingdom system.

See "classification." This is the highest-level grouping of living things. All living things fall into one of three domains: Eukaryotes, Bacteria, and Archaea.

In biology, domain (also superregnum, superkingdom, or empire) is the top-level taxon of organisms in scientific classification, higher than a kingdom. Domain (or its synonyms) is the most inclusive of these biological groupings. The names are arbitrary, but the arrangement reflects the fundamental evolutionary differences in the genomes.