gene: The fundamental physical and functional unit of heredity which carries information from one generation to the next; a segment of DNA, composed of a transcribed region and a regulatory sequence that makes possible transcription.

genome: The entire complement of genetic material in a chromosome set..

chromosome: A linear end-to-end arrangement of genes and other DNA, sometimes with associated protein and RNA.

genotype: The specific allele composition of a cell -- either of the entire cell, or more commonly, for a certain gene or a set of genes.

phenotype: 1) The form taken by some character (or group of characters) in a specific individual. 2) The detectable outward manifestation of a specific genotype.