The term "genome" was proposed by Hans Winkler in 1920 to describe a set of genes contained in a set of chromosomes of one biological species. The term "gene”, in its modern sense, refers to an area of DNA nucleotide sequence encoding the primary structure of one product for its cellular synthesis / production.

The original meaning of the term “genome” was that it, unlike the genotype, constituted a genetic characteristic of the species as a whole, and not of its individuals. With the development of molecular genetics the meaning of the term has changed. It is known that DNA, which is the carrier of genetic information in most organisms and, therefore, is the basis of the genome, includes not only genes in the modern sense of the word. Most DNAs of eukaryotic cells (cells having a nucleus) are represented by non-encoding ("excess") nucleotide sequences that do not contain information about proteins or RNA. The genetic information in the cells is contained not only in the chromosomes of the nucleus, but also in extrachromosomal DNA molecules. In bacteria, such DNAs include plasmids and some moderate viruses, in eukaryotic cells – DNA of mitochondria, chloroplasts and other cell organelles. Therefore, the genome of an organism refers to the total DNA of its chromosome set and of each of the extrachromosomal genetic elements contained in a single cell of the germline of the multicellular organism. Genome size varies considerably among different species, and often there is no correlation between the evolutionary complexity of a biological species and the size of its genome. The science that studies general principles of genome composition, and its structural and functional organisation using methods of sequencing, mapping and functional identification of genes and extragenic elements of various organisms, is called genomics. Methods of genomics focus on deciphering the principles of functioning and evolution of the biological systems and processes of living organisms.