Understanding Genomes: Structure, Variation, Evolution

Definition and scope of genome

In molecular biology and genetics, a genome is the complete set of genetic information carried by an organism. It is primarily defined as the nucleotide sequences of DNA (and RNA in RNA viruses) that make up the organism’s hereditary material. In eukaryotes, the genome typically includes both protein-coding genes and non-coding functional regions (such as regulatory sequences), along with a large fraction of DNA whose function may not be clearly established. The scope of “genome” can vary depending on which molecules are included. For example, bacteria usually have one or two large chromosomal DNA molecules containing essential genetic material, but they may also carry additional extrachromosomal plasmids; in scientific usage, “genome” often refers mainly to the large chromosomal DNA. For eukaryotes, the term is commonly restricted to the nuclear genome, even though mitochondria (and in plants, chloroplasts) contain their own separate genomes. Additionally, because many eukaryotes are diploid, the genome definition must account for multiple chromosome copies—such as including both sex chromosomes (X and Y) in humans when specifying a reference genome.

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Origin of the term genome

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