Hereditary material of a cell is called genome. Physically speaking, it is a DNA, which is contained in one set of chromosomes of an organism. Logically speaking, genome is an assamblage of all genes and sequences, which regulate their expression. Genome occurs in the shape of a mapped continuous sequence of nucleotides. Genome participates in all genetic processes of a cell: heredity is the result of DNA duplication; in the basis of mutations fallings-out, settings-in or replacings of separate nucleotides or small regions lie; action of genes is based on the RNA synthesis. Genome is the molecular basis of the genotype. Investigations of structural and functional organization of the genome are carried out by the science called genomics.