A Google Ngram analysis [6] shows the case-independent occurrence of the terms “gene”, “genome” and “chromosome” in the corpus of books in English from 1920 to 2008. The data are smoothed by a three-year moving average. The term “genome” was coined in 1920 [1], and many sources, including the Oxford English Dictionary, attribute the word to a portmanteau of the words “gene” and “chromosome”, although this etymology is controversial [1]. It took decades for the term to enter common use, and did not reach its current level of use until the turn of the century. Later this year, researchers will finalize the first draft of the entire human genome – the blueprint for life. The size of a genome is not related to the size or complexity of an organism. For example, humans and nematodes (those that are microscopic) have almost the same genome size. Conversely, rice has fewer genes. Therefore, the size of a genome varies between species. For example, invertebrates and birds have relatively small genomes, while amphibians and fish have intermediate genomes. A genome sequence is the complete list of nucleotides (A, C, G and T for DNA genomes) that make up all chromosomes of an individual or species.

Within a species, the vast majority of nucleotides between individuals are identical, but sequencing of several individuals is necessary to understand genetic diversity. It is very difficult to find an exact definition of the “genome”. It usually refers to the DNA (or sometimes RNA) molecules that carry genetic information into an organism, but it is sometimes difficult to decide which molecules to include in the definition. For example, bacteria typically have one or two large DNA molecules (chromosomes) that contain all the essential genetic material, but they also contain smaller extrachromosomal plasmid molecules that carry important genetic information. The definition of “genome” commonly used in the scientific literature is generally limited to large chromosomal DNA molecules of bacteria. [8] On the other hand, the genome of eukaryotes is altered or damaged by the action of mutagens such as ultraviolet radiation, resulting in a functional, structural or physical modification of the genome or a gene. Genome sequencing and genetic mapping are different technologies. However, both can achieve the same results. One of the goals of the Human Genome Project was to create a series of high-resolution chromosome maps. The genome is often described as an organization`s information bank. Whether it is millions or billions of letters of DNA, their transmission over generations is the main means of heredity of the body`s traits. Several emerging areas of research show that this definition is too simplistic.

Here, we explore how a deeper understanding of genomic diversity and cell physiology challenges concepts of the physical permanence of the genome, as well as its role as the sole source of information for an organism. The genetic order, i.e. the distance between genes on chromosomes, and other markers is described in a map of the genome. Genomic maps are available in different resolution or scaling ranges. Physical maps are available to describe the chemical properties of DNA. Genetic maps are useful for recognizing unique inherited traits among chromosomes as genetic markers. However, only polymorphic markers are used in mapping as they are easily recognizable between different individuals. If printed at a distance of 1 mm, the DNA letters in your genome would stretch 3,000 km. Non-coding sequences include introns, sequences for non-coding RNAs, regulatory regions, and repetitive DNA. Non-coding sequences account for 98% of the human genome.

There are two categories of repetitive DNA in the genome: tandem repeats and intercalated repeats. [34] With a better understanding of genomic content, diversity and expression, we can now reassess our fundamental understanding of the genome and its role in the cell. A closer look at the NIH definition, for example, shows that their two halves are mutually exclusive. That is, the “complete set of DNA” cannot be “all the information necessary to build and maintain (a) organism.” Of course, this should probably be a simplified definition for scientists and non-scientists alike. While it is useful to continue to think of the genome as a physical entity encoding the information needed to maintain and replicate an organism, our current understanding shows that this definition is incomplete. For the continuity of life, the genome is transferred from one cell to another during cell replication and differentiation to ensure the preservation of life. The genome has functional, structural and adaptable roles. It is passed down from generation to generation to preserve species. Federal funding has helped achieve scientific breakthroughs such as the Human Genome Project.

Eukaryotic genomes are even more difficult to define because almost all eukaryotic species contain nuclear chromosomes and extra DNA molecules in the mitochondria. In addition, algae and plants have chloroplast DNA. Most textbooks distinguish between the nuclear genome and the genomes of organelles (mitochondria and chloroplasts), so that when they talk about the human genome, for example, they refer only to the genetic material of the nucleus. [2] [9] This is the most common use of the word “genome” in the scientific literature. Viruses are widespread on Earth, they have the ability to infect almost all living organisms, including animals, plants, insects and other living cells. Viruses play a major role in ecology, which can affect the climate. Viruses contain nucleic acids covered with a packet of proteins. They can enter the cell and use its machinery to replicate its genome. The viral genome varies greatly in terms of nucleic acid type, complexity, size and routes of transmission.

The viral genome may be: Non-long terminal repeats (non-LTR) are classified into long intercalated nuclear elements (LINE), short intercalated nuclear elements (SINE) and penelope-like elements (PLE). In Dictyostelium discoideum, there are other DIRS elements that belong to non-LTRs. Non-LTRs are widespread in eukaryotic genomes. [44] The Human Genome Project is unlocking the genetic secrets of life. These examples of physical transivity in genomes show that the chemical composition and stability of a genome are not necessarily fixed requirements in every organism at all times. Synthetic biologists have further demonstrated this point by the chemical synthesis of viral [21,22] and bacterial genomes [23]. Before the chemical synthesis of these DNA chromosomes, genomes were present in a purely informative state in the form of nucleotide sequences in a computer file. In these cases, the genome of the virus or cell is not transferred from one type of nucleic acid to another, but from a physical DNA molecule to a non-physical nucleotide sequence and again to a physical DNA molecule. Although this example is not a natural phenomenon, it provides simple evidence that the informational content of the genome is more important than its physical permanence.

Therefore, the concept of informational supremacy used to define genomes, for example “all the information necessary for the construction and maintenance of this organism”, deserves further investigation. Most eukaryotes are diploid, meaning that there are two copies of each chromosome in the nucleus, but the “genome” refers to only one copy of each chromosome. Some eukaryotes have distinctive sex chromosomes such as mammalian X and Y chromosomes, so the technical definition of the genome must include both copies of the sex chromosomes. For example, if we refer to the standard human reference genome, it consists of one copy each of the 22 autosomes plus one X chromosome and one Y chromosome. [10] There are many huge differences in size in genomes, which have already been mentioned in multicellular eukaryotic genomes. This is largely due to the different abundances of transposable elements that evolve by creating new copies of themselves in chromosomes. [31] Eukaryotic genomes often contain several thousand copies of these elements, most of which have acquired mutations that make them defective. Here is a table of some significant or representative genomes. See also #See for lists of sequenced genomes.

Many biologists already know that the genome is not always best defined as “all the information necessary to build and maintain a cell or organism.” While this definition is useful to the public in the context of an online glossary, it is necessarily an oversimplification. But if a genome is not a complete set of DNA that contains all the information needed to build and maintain the organism, what is? In summary, DNA contains all the information responsible for building the whole body by providing the necessary instructions for the production of proteins. Each gene in the genome (about 20,000 to 25,000 genes) encodes about 3 proteins.