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In classical genetics, the genome of a diploid organism including eukarya refers to a full set of chromosomes or genes in a gamete; thereby, a regular somatic cell contains two full sets of genomes. In haploid organisms, including bacteria, archaea, viruses, and mitochondria, a cell contains only a single set of the genome, usually in a single circular or contiguous linear DNA (or RNA for retroviruses). In modern molecular biology the genome of an organism is its hereditary information encoded in DNA (or, for retroviruses, RNA).

The genome includes both the genes and the non-coding sequences of the DNA.[1] The term was adapted in 1920 by Hans Winkler, Professor of Botany at the University of Hamburg, Germany. The Oxford English Dictionary suggests the name to be a portmanteau of the words gene and chromosome; however, many related -ome words already existed, such as biome and rhizome, forming a vocabulary into which genome fits systematically.[2]

More precisely, the genome of an organism is a complete genetic sequence on one set of chromosomes; for example, one of the two sets that a diploid individual carries in every somatic cell. The term genome can be applied specifically to mean that stored on a complete set of nuclear DNA (i.e., the "nuclear genome") but can also be applied to that stored within organelles that contain their own DNA, as with the mitochondrial genome or the chloroplast genome. Additionally, the genome can comprise nonchromosomal genetic elements such as viruses, plasmids, and transposable elements[3]. When people say that the genome of a sexually reproducing species has been "sequenced", typically they are referring to a determination of the sequences of one set of autosomes and one of each type of sex chromosome, which together represent both of the possible sexes. Even in species that exist in only one sex, what is described as "a genome sequence" may be a composite read from the chromosomes of various individuals. In general use, the phrase "genetic makeup" is sometimes used conversationally to mean the genome of a particular individual or organism. The study of the global properties of genomes of related organisms is usually referred to as genomics, which distinguishes it from genetics which generally studies the properties of single genes or groups of genes.

Both the number of base pairs and the number of genes vary widely from one species to another, and there is little connection between the two (an observation known as the C-value paradox). At present, the highest known number of genes is around 60,000, for the protozoan causing trichomoniasis (see List of sequenced eukaryotic genomes), almost three times as many as in the human genome.

An analogy to the human genome stored on DNA is that of instructions stored in a book:

  • The book would be over one billion words long;
  • The book would be bound in 5000 volumes, each one 300 pages long;
  • The book fits into a cell nucleus the size of a pinpoint;
  • A copy of the book (all 5000 volumes) is contained in almost every cell.



Most biological entities that are more complex than a virus sometimes or always carry additional genetic material besides that which resides in their chromosomes. In some contexts, such as sequencing the genome of a pathogenic microbe, "genome" is meant to include information stored on this auxiliary material, which is carried in plasmids. In such circumstances then, "genome" describes all of the genes and information on non-coding DNA that have the potential to be present.

In eukaryotes such as plants, protozoa and animals, however, "genome" carries the typical connotation of only information on chromosomal DNA. So although these organisms contain mitochondria that have their own DNA, the genes in this mitochondrial DNA are not considered part of the genome. In fact, mitochondria are sometimes said to have their own genome, often referred to as the "mitochondrial genome".

Genomes and genetic variation

Note that a genome does not capture the genetic diversity or the genetic polymorphism of a species. For example, the human genome sequence in principle could be determined from just half the information on the DNA of one cell from one individual. To learn what variations in genetic information underlie particular traits or diseases requires comparisons across individuals. This point explains the common usage of "genome" (which parallels a common usage of "gene") to refer not to the information in any particular DNA sequence, but to a whole family of sequences that share a biological context.

Although this concept may seem counter intuitive, it is the same concept that says there is no particular shape that is the shape of a cheetah. Cheetahs vary, and so do the sequences of their genomes. Yet both the individual animals and their sequences share commonalities, so one can learn something about cheetahs and "cheetah-ness" from a single example of either.

Sequencing and mapping

The Human Genome Project was organized to map and to sequence the human genome. Other genome projects include mouse, rice, the plant Arabidopsis thaliana, the puffer fish, bacteria like E. coli, etc. In 1976, Walter Fiers at the University of Ghent (Belgium) was the first to establish the complete nucleotide sequence of a viral RNA-genome (bacteriophage MS2). The first DNA-genome project to be completed was the Phage Φ-X174, with only 5368 base pairs, which was sequenced by Fred Sanger in 1977 . The first bacterial genome to be completed was that of Haemophilus influenzae, completed by a team at The Institute for Genomic Research in 1995.

The development of new technologies has dramatically decreased the difficulty and cost of sequencing, and the number of complete genome sequences is rising rapidly. Among many genome database sites, the one maintained by the US National Institutes of Health is inclusive.[4]

These new technologies open up the prospect of personal genome sequencing as an important diagnostic tool. A major step toward that goal was the May 2007 New York Times announcement that the full genome of DNA pioneer James D. Watson was deciphered.[5]

Whereas a genome sequence lists the order of every DNA base in a genome, a genome map identifies the landmarks. A genome map is less detailed than a genome sequence and aids in navigating around the genome.[6][7]

Comparison of different genome sizes

Organism type Organism Genome size (base pairs) Note
Virus Bacteriophage MS2 3,569 First sequenced RNA-genome[8]
Virus SV40 5,224 [9]
Virus Phage Φ-X174 5,386 First sequenced DNA-genome[10]
Virus Phage λ 48,502
Bacterium Haemophilus influenzae 1,830,000 First genome of living organism, July 1995[11]
Bacterium Carsonella ruddii 159,662 Smallest non-viral genome.[12]
Bacterium Buchnera aphidicola 600,000
Bacterium Wigglesworthia glossinidia 700,000
Bacterium Escherichia coli 4,600,000 [13]
Bacterium Solibacter usitatus (strain Ellin 6076) 9,970,000 Largest known Bacterial genome
Amoeba Amoeba dubia 670,000,000,000 Largest known genome.[14]
Plant Arabidopsis thaliana 157,000,000 First plant genome sequenced, December 2000.[15]
Plant Genlisea margaretae 63,400,000 Smallest recorded flowering plant genome, 2006.[15]
Plant Fritillaria assyrica 130,000,000,000
Plant Populus trichocarpa 480,000,000 First tree genome, September 2006
Moss Physcomitrella patens 480,000,000 First genome of a bryophyte, January 2008 [16]
Yeast Saccharomyces cerevisiae 12,100,000 [17]
Fungus Aspergillus nidulans 30,000,000
Nematode Caenorhabditis elegans 98,000,000 First multicellular animal genome, December 1998[18]
Nematode Pratylenchus coffeae 20,000,000 Smallest animal genome known[19]
Insect Drosophila melanogaster (fruit fly) 130,000,000 [20]
Insect Bombyx mori (silk moth) 530,000,000
Insect Apis mellifera (honey bee) 1,770,000,000
Fish Tetraodon nigroviridis (type of puffer fish) 385,000,000 Smallest vertebrate genome known
Mammal Homo sapiens 3,200,000,000
Fish Protopterus aethiopicus (marbled lungfish) 130,000,000,000 Largest vertebrate genome known

Note: The DNA from a single human cell has a length of ~1.8 m (but at a width of ~2.4 nanometers).

Since genomes and their organisms are very complex, one research strategy is to reduce the number of genes in a genome to the bare minimum and still have the organism in question survive. There is experimental work being done on minimal genomes for single cell organisms as well as minimal genomes for multicellular organisms (see Developmental biology). The work is both in vivo and in silico.

Genome evolution

Genomes are more than the sum of an organism's genes and have traits that may be measured and studied without reference to the details of any particular genes and their products. Researchers compare traits such as chromosome number (karyotype), genome size, gene order, codon usage bias, and GC-content to determine what mechanisms could have produced the great variety of genomes that exist today (for recent overviews, see Brown 2002; Saccone and Pesole 2003; Benfey and Protopapas 2004; Gibson and Muse 2004; Reese 2004; Gregory 2005).

Duplications play a major role in shaping the genome. Duplications may range from extension of short tandem repeats, to duplication of a cluster of genes, and all the way to duplications of entire chromosomes or even entire genomes. Such duplications are probably fundamental to the creation of genetic novelty.

Horizontal gene transfer is invoked to explain how there is often extreme similarity between small portions of the genomes of two organisms that are otherwise very distantly related. Horizontal gene transfer seems to be common among many microbes. Also, eukaryotic cells seem to have experienced a transfer of some genetic material from their chloroplast and mitochondrial genomes to their nuclear chromosomes.

See also


  1. ^ Ridley, M. (2006). Genome. New York, NY: Harper Perennial. ISBN 0-06-019497-9
  2. ^ Joshua Lederberg and Alexa T. McCray (2001). "'Ome Sweet 'Omics -- A Genealogical Treasury of Words". The Scientist 15 (7). 
  3. ^ Madigan M, Martinko J (editors) (2006). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1. 
  4. ^
  5. ^
  6. ^
  7. ^
  8. ^ Fiers W, et al. (1976). "Complete nucleotide-sequence of bacteriophage MS2-RNA - primary and secondary structure of replicase gene". Nature 260: 500–507. doi:10.1038/260500a0. PMID 1264203. 
  9. ^ Fiers W, Contreras R, Haegemann G, Rogiers R, Van de Voorde A, Van Heuverswyn H, Van Herreweghe J, Volckaert G, Ysebaert M (1978). "Complete nucleotide sequence of SV40 DNA". Nature 273 (5658): 113–120. doi:10.1038/273113a0. PMID 205802. 
  10. ^ Sanger F, Air GM, Barrell BG, Brown NL, Coulson AR, Fiddes CA, Hutchison CA, Slocombe PM, Smith M (1977). "Nucleotide sequence of bacteriophage phi X174 DNA". Nature 265 (5596): 687–695. doi:10.1038/265687a0. PMID 870828. 
  11. ^ Fleischmann R, Adams M, White O, Clayton R, Kirkness E, Kerlavage A, Bult C, Tomb J, Dougherty B, Merrick J (1995). "Whole-genome random sequencing and assembly of Haemophilus influenzae Rd". Science 269 (5223): 496–512. doi:10.1126/science.7542800. PMID 7542800. 
  12. ^ Nakabachi A, Yamashita A, Toh H, et al. (October 2006). "The 160-kilobase genome of the bacterial endosymbiont Carsonella". Science (journal) 314 (5797): 267. doi:10.1126/science.1134196. PMID 17038615. 
  13. ^ Frederick R. Blattner, Guy Plunkett III, et al. (1997). "The Complete Genome Sequence of Escherichia coli K-12". Science 277: 1453–1462. doi:10.1126/science.277.5331.1453. PMID 9278503. 
  14. ^ Parfrey, L.W.; Lahr, D.J.G.; Katz, L.A. (2008). "The Dynamic Nature of Eukaryotic Genomes". Molecular Biology and Evolution 25 (4): 787. doi:10.1093/molbev/msn032. PMID 18258610. 
  15. ^ a b Greilhuber, J., Borsch, T., Müller, K., Worberg, A., Porembski, S., and Barthlott, W. (2006). "Smallest angiosperm genomes found in Lentibulariaceae, with chromosomes of bacterial size". Plant Biology 8: 770–777. doi:10.1055/s-2006-924101. PMID 17203433. 
  16. ^ Daniel Lang, Andreas D. Zimmer, Stefan A. Rensing, Ralf Reski(2008): Exploring plant biodiversity: the Physcomitrella genome and beyond. Trends in Plant Science 13, 542-549. [1]
  17. ^
  18. ^ The C. elegans Sequencing Consortium (1998). "Genome sequence of the nematode C. elegans: a platform for investigating biology". Science 282 (5396): 2012–2018. doi:10.1126/science.282.5396.2012. PMID 9851916. 
  19. ^ "Gregory, T.R. (2005). Animal Genome Size Database.". 
  20. ^ Adams MD, Celniker SE, Holt RA, et al. (2000). "The genome sequence of Drosophila melanogaster". Science 287 (5461): 2185–95. doi:10.1126/science.287.5461.2185. PMID 10731132. Retrieved on 2007-05-25. 

Further reading

External links


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary




gene +‎ -ome


  • (UK) IPA: /ˈdʒiː.nəʊm/
  • (US) IPA: /ˈdʒiː.noʊm/, /dʒɨˈnoʊm/


Wikipedia has an article on:




genome (plural genomes)

  1. The complete genetic information (either DNA or, in some viruses, RNA) of an organism, typically expressed in number of basepairs.

Derived terms


Simple English

The genome of an organism is the whole of its hereditary information encoded in its DNA (or, for some viruses, RNA). This includes both the genes and the non-coding sequences of the DNA. The term was coined in 1920.[1]

Winkler's definition, in translation, runs:

"I propose the expression Genome for the haploid chromosome set, which, together with the pertinent protoplasm, specifies the material foundations of the species ...." [2]p165

However, no single haploid chromosome set defines even the DNA of a species, because of the huge variety of alleles carried by a population. Even a diploid individual carries genetic variety. For that reason Dobzhansky preferred "set of chromosomes",[3] and the definition now must be broader than Winklers' definition. The genome of a haploid chromosome set is merely a sample of the total genetic variety of a species.

The term genome can be applied specifically to mean the complete set of nuclear DNA (the 'nuclear genome') but can also be used of organelles that contain their own DNA, as with the mitochondrial genome or the chloroplast genome.


Comparison of different genome sizes

Organism Genome size (base pairs) Note
Virus, Bacteriophage MS2 3569 First sequenced RNA-genome[4]
Virus, SV40 5224[5]
Virus, Phage Φ-X174 5386 First sequenced DNA-genome[6]
Virus, Phage λ 5×104
Bacterium, Carsonella ruddii 1.6×105 Smallest non-viral genome, Feb 2007
Bacterium, Buchnera aphidicola 6×105
Bacterium, Wigglesworthia glossinidia 7×105
Bacterium, Escherichia coli 4×106
Amoeba, Amoeba dubia 6.7×1011 Largest known genome, Dec 2005
Plant, Arabidopsis thaliana 1.57×108 First plant genome sequenced, Dec 2000.[7]
Plant, Genlisea margaretae 6.34×107 Smallest recorded flowering plant genome, 2006.[7]
Plant, Fritillaria assyrica 1.3×1011
Plant, Populus trichocarpa 4.8×108 First tree genome, Sept 2006
Yeast, Saccharomyces cerevisiae 2×107
Fungus, Aspergillus nidulans 3×107
Nematode, Caenorhabditis elegans 9.8×107 First multicellular animal genome, December 1998[8]
Insect, Drosophila melanogaster aka fruit fly 1.3×108
Insect, Bombyx mori aka silk moth 5.30×108
Insect, Apis mellifera aka honey bee 1.77×109
Fish, Tetraodon nigroviridis, type of Puffer fish 3.85×108 Smallest vertebrate genome known
Mammal, Homo sapiens 3×109
Fish, Protopterus aethiopicus aka marbled lungfish 1.3×1011 Largest vertebrate genome known

Note: The DNA from a single human cell has a length of ~1.8 m (but at a width of ~2.4 nanometers).

Other pages


  1. by Hans Winkler, Professor of Botany at the University of Hamburg, Germany, as a combination of the words gene and chromosome.Joshua Lederberg and Alexa T. McCray (2001). [Expression error: Unexpected < operator "'Ome Sweet 'Omics -- A genealogical treasury of words"]. The Scientist 15 (7). 
    An online copy is available here: [1]
  2. Winkler H. 1920. Verbreitung und Ursache der Parthenogenesis im Pflanzen- und Tierreiche. Fischer, Jena".
  3. Dobzhansky T. 1937. Genetics and the origin of species. Columbia N.Y.
  4. Fiers W, et al. (1976). [Expression error: Unexpected < operator "Complete nucleotide-sequence of bacteriophage MS2-RNA - primary and secondary structure of replicase gene"]. Nature 260: 500-507. 
  5. Fiers W, Contreras R, Haegemann G, Rogiers R, Van de Voorde A, Van Heuverswyn H, Van Herreweghe J, Volckaert G, Ysebaert M (1978). [Expression error: Unexpected < operator "Complete nucleotide sequence of SV40 DNA"]. Nature 273 (5658): 113-120. 
  6. Sanger F, Air GM, Barrell BG, Brown NL, Coulson AR, Fiddes CA, Hutchison CA, Slocombe PM, Smith M (1977). [Expression error: Unexpected < operator "Nucleotide sequence of bacteriophage phi X174 DNA"]. Nature 265 (5596): 687-695. 
  7. 7.0 7.1 Greilhuber J. et al 2006. Smallest angiosperm genomes found in Lentibulariaceae, with chromosomes of bacterial size. Plant Biology. 8: 770-777.
  8. The C. elegans Sequencing Consortium (1998). "Genome sequence of the nematode C. elegans: a platform for investigating biology". Science 282: 2012–2018. 
  • Benfey P. and Protopapas A.D. 2004. Essentials of genomics. Prentice Hall.
  • Brown T.A. 2002. Genomes 2. Bios Scientific Publishers.
  • Gibson G. and Muse S.V. 2004. A primer of genome science. 2nd ed. Sinauer Assoc.
  • Gregory T.R. (ed) 2005. The evolution of the genome. Elsevier.
  • Reece R.J. 2004. Analysis of genes and genomes. Wiley.
  • Saccone C. and Pesole G. 2003. Handbook of comparative genomics. Wiley.
  • Werner E. 2003. In silico multicellular systems biology and minimal genomes. Drug Discov Today. 8(24):1121-7. PubMed
  • Witzany G. 2007. Natural genome editing competences of viruses. Acta Biotheoretica. [2]

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