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Molecular Basis of Heredity: Part 2. Genomes

Author(s): Raye L. Alford, PhD

Overlapping Genes

The genes within an organism's genome are generally not evenly distributed along the length of that organism's DNA. The genes of mitochondria, bacteria and viruses often are immediately adjacent to one another, and frequently overlap. In eukaryotes, there are gene-rich and gene-poor regions within the genome where non-coding spacer regions span the distance between gene-rich areas. Within the gene-rich areas, overlapping genes are common. Overlapping genes are different genes whose nucleotide sequences overlap along a segment of DNA. The nucleotide sequence of overlapping genes is read by RNA polymerases in two or more reading frames or from opposite strands of the DNA molecule, thereby encoding different proteins within the same segment of DNA. Overlapping genes are found throughout nature, from bacteria and viruses to mammals, including humans.