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A segment of coding DNA (DNA that instructs the structure and function of cells throughout the body) composed of a specific sequence of nucleotides. The gene is the basic unit of inheritance that directs every facet of the body’s appearance and functions. Genes align along chromosomes in pairs. Each CHROMOSOME (AUTOSOME) contains thousands of genes, except the sex chromosomes which contain only a few hundred genes.
Each gene has a specific location on the chromosome, called its locus, and encodes a specific function (either a protein or RNA transcription). The HUMAN GENOME PROJECT identified 19,599 confirmed genes and 2,188 probable genes at its conclusion in April 2003. GENETIC DISORDERS occur when there are disruptions of the ALLELE pairings or there is damage to the gene or the chromosome at or near the gene’s locus.
Each gene has a specific task, which it carries out through a process called encoding. The gene instructs the cells to synthesize (produce) a specific protein. Ribosomes, specialized structures within each cell, synthesize the proteins. The protein then carries the gene’s message to its target and initiates the appropriate sequence of biochemical events to implement the message.
For further discussion of genes within the context of the structures and functions of genetics, please see the overview section “Genetics and Molecular Medicine.”