Chromosome

A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being very strongly stained by particular dyes.

Diagram of a replicated and condensed metaphase eukaryotic chromosome. (1) Chromatid – one of the two identical parts of the chromosome after S phase. (2) Centromere – the point where the two chromatids touch, and where the microtubules attach. (3) Short arm. (4) Long arm.

Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 10,000 to 1,000,000,000[1] nucleotides in a long chain. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example, mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.

In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the very long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes are the essential unit for cellular division and must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of their progeny. Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, whereas duplicated chromosomes (copied during synthesis phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right). Chromosomal recombination plays a vital role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe and die, or it may aberrantly evade apoptosis leading to the progression of cancer.

In practice "chromosome" is a rather loosely defined term. In prokaryotes and viruses, the term genophore is more appropriate when no chromatin is present. However, a large body of work uses the term chromosome regardless of chromatin content. In prokaryotes DNA is usually arranged as a circle, which is tightly coiled in on itself, sometimes accompanied by one or more smaller, circular DNA molecules called plasmids. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest genophores are found in viruses: these DNA or RNA molecules are short linear or circular genophores that often lack structural proteins.

Contents

History

Chromosomes as vectors of heredity

In a series of experiments, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity. His two principles were based upon the continuity of chromosomes and the individuality of chromosomes.

It is the second of these principles that was so original. Boveri was able to test the proposal put forward by Wilhelm Roux, that each chromosome carries a different genetic load, and showed that Roux was right. Upon the rediscovery of Mendel, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes. It is interesting to see that Boveri influenced two generations of American cytologists: Edmund Beecher Wilson, Walter Sutton and Theophilus Painter were all influenced by Boveri (Wilson and Painter actually worked with him).

In his famous textbook The Cell, Wilson linked Boveri and Sutton together by the Boveri-Sutton theory. Mayr remarks that the theory was hotly contested by some famous geneticists: William Bateson, Wilhelm Johannsen, Richard Goldschmidt and T.H. Morgan, all of a rather dogmatic turn-of-mind. Eventually complete proof came from chromosome maps in Morgan's own lab.[2]

Chromosomes in eukaryotes

Eukaryotes (cells with nuclei such as those found in plants, yeast, and animals) possess multiple large linear chromosomes contained in the cell's nucleus. Each chromosome has one centromere, with one or two arms projecting from the centromere, although, under most circumstances, these arms are not visible as such. In addition, most eukaryotes have a small circular mitochondrial genome, and some eukaryotes may have additional small circular or linear cytoplasmic chromosomes.

In the nuclear chromosomes of eukaryotes, the uncondensed DNA exists in a semi-ordered structure, where it is wrapped around histones (structural proteins), forming a composite material called chromatin.

Chromatin

Chromatin is the complex of DNA and protein found in the eukaryotic nucleus, which packages chromosomes. The structure of chromatin varies significantly between different stages of the cell cycle, according to the requirements of the DNA.

Interphase chromatin

During interphase (the period of the cell cycle where the cell is not dividing), two types of chromatin can be distinguished:

Individual chromosomes cannot be distinguished at this stage – they appear in the nucleus as a homogeneous tangled mix of DNA and protein.

Metaphase chromatin and division

See also: mitosis and meiosis
Human chromosomes during metaphase.

In the early stages of mitosis or meiosis (cell division), the chromatin strands become more and more condensed. They cease to function as accessible genetic material (transcription stops) and become a compact transportable form. This compact form makes the individual chromosomes visible, and they form the classic four arm structure, a pair of sister chromatids attached to each other at the centromere. The shorter arms are called p arms (from the French petit, small) and the longer arms are called q arms (q follows p in the Latin alphabet). This is the only natural context in which individual chromosomes are visible with an optical microscope.

During divisions, long microtubules attach to the centromere and the two opposite ends of the cell. The microtubules then pull the chromatids apart, so that each daughter cell inherits one set of chromatids. Once the cells have divided, the chromatids are uncoiled and can function again as chromatin. In spite of their appearance, chromosomes are structurally highly condensed, which enables these giant DNA structures to be contained within a cell nucleus (Fig. 2).

The self-assembled microtubules form the spindle, which attaches to chromosomes at specialized structures called kinetochores, one of which is present on each sister chromatid. A special DNA base sequence in the region of the kinetochores provides, along with special proteins, longer-lasting attachment in this region.

Chromosomes in prokaryotes

The prokaryotes – bacteria and archaea – typically have a single circular chromosome, but many variations do exist.[3] Most bacteria have a single circular chromosome that can range in size from only 160,000 base pairs in the endosymbiotic bacterium Candidatus Carsonella ruddii,[4] to 12,200,000 base pairs in the soil-dwelling bacterium Sorangium cellulosum.[5] Spirochaetes of the genus Borrelia are a notable exception to this arrangement, with bacteria such as Borrelia burgdorferi, the cause of Lyme disease, containing a single linear chromosome.[6]

Structure in sequences

Prokaryotic chromosomes have less sequence-based structure than eukaryotes. Bacteria typically have a single point (the origin of replication) from which replication starts, whereas some archaea contain multiple replication origins.[7] The genes in prokaryotes are often organized in operons, and do not usually contain introns, unlike eukaryotes.

DNA packaging

Prokaryotes do not possess nuclei. Instead, their DNA is organized into a structure called the nucleoid.[8] The nucleoid is a distinct structure and occupies a defined region of the bacterial cell. This structure is, however, dynamic and is maintained and remodeled by the actions of a range of histone-like proteins, which associate with the bacterial chromosome.[9] In archaea, the DNA in chromosomes is even more organized, with the DNA packaged within structures similar to eukaryotic nucleosomes.[10][11]

Bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria. In molecular biology application, this allows for its isolation from plasmid DNA by centrifugation of lysed bacteria and pelleting of the membranes (and the attached DNA).

Prokaryotic chromosomes and plasmids are, like eukaryotic DNA, generally supercoiled. The DNA must first be released into its relaxed state for access for transcription, regulation, and replication.

Fig. 2: The major structures in DNA compaction; DNA, the nucleosome, the 10nm "beads-on-a-string" fibre, the 30nm fibre and the metaphase chromosome.

Number of chromosomes in various organisms

Eukaryotes

These tables give the total number of chromosomes (including sex chromosomes) in a cell nucleus. For example, human cells are diploid and have 22 different types of autosome, each present as two copies, and two sex chromosomes. This gives 46 chromosomes in total. Other organisms have more than two copies of their chromosomes, such as bread wheat, which is hexaploid and has six copies of seven different chromosomes – 42 chromosomes in total.

Chromosome numbers in some plants
Plant Species #
Arabidopsis thaliana (diploid)[12] 10
Rye (diploid)[13] 14
Maize (diploid or palaeotetraploid)[14] 20
Einkorn wheat (diploid)[15] 14
Durum wheat (tetraploid)[15] 28
Bread wheat (hexaploid)[15] 42
Cultivated tobacco (tetraploid)[16] 48
Adder's Tongue Fern (diploid)[17] approx 1,400
Chromosome numbers (2n) in some animals
Species # Species #
Common fruit fly 8 Guinea Pig[18] 64
Guppy (poecilia reticulata)[19] 46 Garden snail[20] 54
Earthworm (Octodrilus complanatus)[21] 36 Tibetan fox 36
Domestic cat[22] 38 Domestic pig 38
Laboratory mouse[23][24] 40 Laboratory rat[24] 42
Rabbit (Oryctolagus cuniculus)[25] 44 Syrian hamster[23] 44
Hares[26][27] 48 Human[28] 46
Gorillas, Chimpanzees[28] 48 Domestic sheep 54
Elephants[29] 56 Cow 60
Donkey 62 Horse 64
Dog[30] 78 Kingfisher[31] 132
Goldfish[32] 100-104 Silkworm[33] 56
Chromosome numbers in other organisms
Species Large
Chromosomes		 Intermediate
Chromosomes		 Microchromosomes
Trypanosoma brucei 11 6 ~100
Domestic Pigeon (Columba livia domestics)[34] 18 - 59-63
Chicken[35] 8 2 sex chromosomes 60

Normal members of a particular eukaryotic species all have the same number of nuclear chromosomes (see the table). Other eukaryotic chromosomes, i.e., mitochondrial and plasmid-like small chromosomes, are much more variable in number, and there may be thousands of copies per cell.

The 23 human chromosome territories during prometaphase in fibroblast cells.

Asexually reproducing species have one set of chromosomes, which are the same in all body cells. However, asexual species can be either haploid or diploid.

Sexually reproducing species have somatic cells (body cells), which are diploid [2n] having two sets of chromosomes, one from the mother and one from the father. Gametes, reproductive cells, are haploid [n]: They have one set of chromosomes. Gametes are produced by meiosis of a diploid germ line cell. During meiosis, the matching chromosomes of father and mother can exchange small parts of themselves (crossover), and thus create new chromosomes that are not inherited solely from either parent. When a male and a female gamete merge (fertilization), a new diploid organism is formed.

Some animal and plant species are polyploid [Xn]: They have more than two sets of homologous chromosomes. Plants important in agriculture such as tobacco or wheat are often polyploid, compared to their ancestral species. Wheat has a haploid number of seven chromosomes, still seen in some cultivars as well as the wild progenitors. The more-common pasta and bread wheats are polyploid, having 28 (tetraploid) and 42 (hexaploid) chromosomes, compared to the 14 (diploid) chromosomes in the wild wheat.[36]

Prokaryotes

Prokaryote species generally have one copy of each major chromosome, but most cells can easily survive with multiple copies.[37] For example, Buchnera, a symbiont of aphids has multiple copies of its chromosome, ranging from 10–400 copies per cell.[38] However, in some large bacteria, such as Epulopiscium fishelsoni up to 100,000 copies of the chromosome can be present.[39] Plasmids and plasmid-like small chromosomes are, as in eukaryotes, very variable in copy number. The number of plasmids in the cell is almost entirely determined by the rate of division of the plasmid – fast division causes high copy number, and vice versa.

Karyotype

Main article: Karyotype
Figure 3: Karyogram of a human male

In general, the karyotype is the characteristic chromosome complement of a eukaryote species.[40] The preparation and study of karyotypes is part of cytogenetics.

Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karyotypes, which are often highly variable. There may be variation between species in chromosome number and in detailed organization. In some cases, there is significant variation within species. Often there is:

1. variation between the two sexes
2. variation between the germ-line and soma (between gametes and the rest of the body)
3. variation between members of a population, due to balanced genetic polymorphism
4. geographical variation between races
5. mosaics or otherwise abnormal individuals.

Also, variation in karyotype may occur during development from the fertilised egg.

The technique of determining the karyotype is usually called karyotyping. Cells can be locked part-way through division (in metaphase) in vitro (in a reaction vial) with colchicine. These cells are then stained, photographed, and arranged into a karyogram, with the set of chromosomes arranged, autosomes in order of length, and sex chromosomes (here X/Y) at the end: Fig. 3.

Like many sexually reproducing species, humans have special gonosomes (sex chromosomes, in contrast to autosomes). These are XX in females and XY in males.

Historical note

Investigation into the human karyotype took many years to settle the most basic question. How many chromosomes does a normal diploid human cell contain? In 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia, concluding an XX/XO sex determination mechanism.[41] Painter in 1922 was not certain whether the diploid number of man is 46 or 48, at first favouring 46.[42] He revised his opinion later from 46 to 48, and he correctly insisted on man's having an XX/XY system.[43]

New techniques were needed to definitively solve the problem:

1. Using cells in culture
2. Pretreating cells in a hypotonic solution, which swells them and spreads the chromosomes
3. Arresting mitosis in metaphase by a solution of colchicine
4. Squashing the preparation on the slide forcing the chromosomes into a single plane
5. Cutting up a photomicrograph and arranging the result into an indisputable karyogram.

It took until the mid-1950s for it to become generally accepted that the human karyotype include only 46 chromosomes. Considering the techniques of Winiwarter and Painter, their results were quite remarkable.[44][45] Chimpanzees (the closest living relatives to modern humans) have 48 chromosomes.

Chromosomal aberrations

Main articles: Chromosome abnormality and aneuploidy
The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The two major two-chromosome mutations; insertion (1) and translocation (2).
In Down syndrome, there are three copies of chromosome 21

Chromosomal aberrations are disruptions in the normal chromosomal content of a cell, and are a major cause of genetic conditions in humans, such as Down syndrome. Some chromosome abnormalities do not cause disease in carriers, such as translocations, or chromosomal inversions, although they may lead to a higher chance of birthing a child with a chromosome disorder. Abnormal numbers of chromosomes or chromosome sets, aneuploidy, may be lethal or give rise to genetic disorders. Genetic counseling is offered for families that may carry a chromosome rearrangement.

The gain or loss of DNA from chromosomes can lead to a variety of genetic disorders. Human examples include:

Chromosomal mutations produce changes in whole chromosomes (more than one gene) or in the number of chromosomes present.

Most mutations are neutral – have little or no effect. Chromosomal aberrations are the changes in the structure of chromosomes. It has a great role in evolution. A detailed graphical display of all human chromosomes and the diseases annotated at the correct spot may be found at the Oak Ridge National Laboratory.[48]

Human chromosomes

Chromosomes can be divided into two types--autosomes, and sex chromosomes. Certain genetic traits are linked to your sex, and are passed on through the sex chromosomes. The autosomes contain the rest of the genetic hereditary information. All act in the same way during cell division. Human cells have 23 pairs of large linear nuclear chromosomes, (22 pairs of autosomes and one pair of sex chromosomes) giving a total of 46 per cell. In addition to these, human cells have many hundreds of copies of the mitochondrial genome. Sequencing of the human genome has provided a great deal of information about each of the chromosomes. Below is a table compiling statistics for the chromosomes, based on the Sanger Institute's human genome information in the Vertebrate Genome Annotation (VEGA) database.[49] Number of genes is an estimate as it is in part based on gene predictions. Total chromosome length is an estimate as well, based on the estimated size of unsequenced heterochromatin regions.

Genes and bases on chromosomes.png

Chromosome Genes Total bases Sequenced bases[50]
1 4,220 247,199,719 224,999,719
2 1,491 242,751,149 237,712,649
3 1,550 199,446,827 194,704,827
4 446 191,263,063 187,297,063
5 609 180,837,866 177,702,766
6 2,281 170,896,993 167,273,993
7 2,135 158,821,424 154,952,424
8 1,106 146,274,826 142,612,826
9 1,920 140,442,298 120,312,298
10 1,793 135,374,737 131,624,737
11 379 134,452,384 131,130,853
12 1,430 132,289,534 130,303,534
13 924 114,127,980 95,559,980
14 1,347 106,360,585 88,290,585
15 921 100,338,915 81,341,915
16 909 88,822,254 78,884,754
17 1,672 78,654,742 77,800,220
18 519 76,117,153 74,656,155
19 1,555 63,806,651 55,785,651
20 1,008 62,435,965 59,505,254
21 578 46,944,323 34,171,998
22 1,092 49,528,953 34,893,953
X (sex chromosome) 1,846 154,913,754 151,058,754
Y (sex chromosome) 454 57,741,652 25,121,652
Total 32,185 3,079,843,747 2,857,698,560

See also

References

  1. ↑ Paux E, Sourdille P, Salse J, et al. (2008). "A Physical Map of the 1-Gigabase Bread Wheat Chromosome 3B". Science 322 (5898): 101–104. doi:10.1126/science.1161847. PMID 18832645. 
  2. ↑ Mayr E. 1982. The growth of biological thought. Harvard. p749
  3. ↑ Thanbichler M, Shapiro L (2006). "Chromosome organization and segregation in bacteria". J. Struct. Biol. 156 (2): 292–303. doi:10.1016/j.jsb.2006.05.007. PMID 16860572. 
  4. ↑ Nakabachi A, Yamashita A, Toh H, Ishikawa H, Dunbar H, Moran N, Hattori M (2006). "The 160-kilobase genome of the bacterial endosymbiont Carsonella". Science 314 (5797): 267. doi:10.1126/science.1134196. PMID 17038615. 
  5. ↑ Pradella S, Hans A, Spröer C, Reichenbach H, Gerth K, Beyer S (2002). "Characterisation, genome size and genetic manipulation of the myxobacterium Sorangium cellulosum So ce56". Arch Microbiol 178 (6): 484–92. doi:10.1007/s00203-002-0479-2. PMID 12420170. 
  6. ↑ Hinnebusch J, Tilly K (1993). "Linear plasmids and chromosomes in bacteria". Mol Microbiol 10 (5): 917–22. doi:10.1111/j.1365-2958.1993.tb00963.x. PMID 7934868. 
  7. ↑ Kelman LM, Kelman Z (2004). "Multiple origins of replication in archaea". Trends Microbiol. 12 (9): 399–401. doi:10.1016/j.tim.2004.07.001. PMID 15337158. 
  8. ↑ Thanbichler M, Wang SC, Shapiro L (2005). "The bacterial nucleoid: a highly organized and dynamic structure". J. Cell. Biochem. 96 (3): 506–21. doi:10.1002/jcb.20519. PMID 15988757. 
  9. ↑ Sandman K, Pereira SL, Reeve JN (1998). "Diversity of prokaryotic chromosomal proteins and the origin of the nucleosome". Cell. Mol. Life Sci. 54 (12): 1350–64. doi:10.1007/s000180050259. PMID 9893710. 
  10. ↑ Sandman K, Reeve JN (2000). "Structure and functional relationships of archaeal and eukaryal histones and nucleosomes". Arch. Microbiol. 173 (3): 165–9. doi:10.1007/s002039900122. PMID 10763747. 
  11. ↑ Pereira SL, Grayling RA, Lurz R, Reeve JN (1997). "Archaeal nucleosomes". Proc. Natl. Acad. Sci. U.S.A. 94 (23): 12633–7. doi:10.1073/pnas.94.23.12633. PMID 9356501. PMC 25063. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=9356501. 
  12. ↑ Armstrong SJ, Jones GH (January 2003). "Meiotic cytology and chromosome behaviour in wild-type Arabidopsis thaliana". J. Exp. Bot. 54 (380): 1–10. doi:10.1093/jxb/54.380.1. PMID 12456750. http://jexbot.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=12456750. 
  13. ↑ Gill BS, Kimber G (April 1974). "The Giemsa C-banded karyotype of rye". Proc. Natl. Acad. Sci. U.S.A. 71 (4): 1247–9. doi:10.1073/pnas.71.4.1247. PMID 4133848. 
  14. ↑ Kato A, Lamb JC, Birchler JA (September 2004). "Chromosome painting using repetitive DNA sequences as probes for somatic chromosome identification in maize". Proc. Natl. Acad. Sci. U.S.A. 101 (37): 13554–9. doi:10.1073/pnas.0403659101. PMID 15342909. PMC 518793. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=15342909. 
  15. ↑ 15.0 15.1 15.2 Dubcovsky J, Luo MC, Zhong GY, et al. (1996). "Genetic map of diploid wheat, Triticum monococcum L., and its comparison with maps of Hordeum vulgare L". Genetics 143 (2): 983–99. PMID 8725244. 
  16. ↑ Kenton A, Parokonny AS, Gleba YY, Bennett MD (August 1993). "Characterization of the Nicotiana tabacum L. genome by molecular cytogenetics". Mol. Gen. Genet. 240 (2): 159–69. doi:10.1007/BF00277053. PMID 8355650. 
  17. ↑ Leitch IJ, Soltis DE, Soltis PS, Bennett MD (2005). "Evolution of DNA amounts across land plants (embryophyta)". Ann. Bot. 95 (1): 207–17. doi:10.1093/aob/mci014. PMID 15596468. http://aob.oxfordjournals.org/cgi/content/full/95/1/207. 
  18. ↑ Umeko Semba, Yasuko Umeda, Yoko Shibuya, Hiroaki Okabe, Sumio Tanase and Tetsuro Yamamoto (2004). "Primary structures of guinea pig high- and low-molecular-weight kininogens". International Immunopharmacology 4 (10-11): 1391–1400. doi:10.1016/j.intimp.2004.06.003. PMID 15313436. http://www.sciencedirect.com/science/article/B6W7N-4CX6PRC-1/2/97487fdf611a04e3c88690da9e6d853b. 
  19. ↑ "The Genetics of the Popular Aquarium Pet - Guppy Fish". http://fancyguppy.webs.com/genetics.htm. Retrieved 2009-12-06. 
  20. ↑ Vitturi R, Libertini A, Sineo L, et al. (2005). "Cytogenetics of the land snails Cantareus aspersus and C. mazzullii (Mollusca: Gastropoda: Pulmonata)". Micron 36 (4): 351–7. doi:10.1016/j.micron.2004.12.010. PMID 15857774. 
  21. ↑ Vitturi R, Colomba MS, Pirrone AM, Mandrioli M (2002). "rDNA (18S-28S and 5S) colocalization and linkage between ribosomal genes and (TTAGGG)(n) telomeric sequence in the earthworm, Octodrilus complanatus (Annelida: Oligochaeta: Lumbricidae), revealed by single- and double-color FISH". J. Hered. 93 (4): 279–82. doi:10.1093/jhered/93.4.279. PMID 12407215. http://jhered.oxfordjournals.org/cgi/content/full/93/4/279. 
  22. ↑ Nie W, Wang J, O'Brien PC, et al. (2002). "The genome phylogeny of domestic cat, red panda and five mustelid species revealed by comparative chromosome painting and G-banding". Chromosome Res. 10 (3): 209–22. doi:10.1023/A:1015292005631. PMID 12067210. 
  23. ↑ 23.0 23.1 Romanenko, Svetlana A; Polina L Perelman, Natalya A Serdukova, Vladimir A Trifonov, Larisa S Biltueva, Jinhuan Wang, Tangliang Li, Wenhui Nie, Patricia C. M. O'Brien, Vitaly T. Volobouev, Roscoe Stanyon, Malcolm A. Ferguson-Smith, Fengtang Yang, Alexander S. Graphodatsky (2006-12). "Reciprocal chromosome painting between three laboratory rodent species". Mammalian Genome: Official Journal of the International Mammalian Genome Society 17 (12): 1183–1192. doi:10.1007/s00335-006-0081-z. ISSN 0938-8990. PMID 17143584. http://www.ncbi.nlm.nih.gov/pubmed/17143584. Retrieved 2009-10-14. 
  24. ↑ 24.0 24.1 A Comparison of the chromosomes of the rat and mouse with reference to the question of chromosome homology in mammals
  25. ↑ Hayes, H.; C. Rogel-Gaillard, C. Zijlstra, N.A. de Haan, C. Urien, N. Bourgeaux, M. Bertaud, A.A. Bosma (2002). "Establishment of an R-banded rabbit karyotype nomenclature by FISH localization of 23 chromosome-specific genes on both G- and R-banded chromosomes". Cytogenetic and Genome Research 98 (2-3): 199–205. doi:10.1159/000069807. ISSN 1424-859X. PMID 12698004. http://content.karger.com/produktedb/produkte.asp?typ=fulltext&file=CGR98199. Retrieved 2009-10-14. 
  26. ↑ T.J. Robinson, F. Yang, W.R. Harrison (2002). "Chromosome painting refines the history of genome evolution in hares and rabbits (order Lagomorpha)". Cytogenic and Genetic Research 96 (1-4): 223–227. doi:10.1159/000063034. PMID 12438803. http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowAbstract&ArtikelNr=63034&Ausgabe=228416&ProduktNr=224037. 
  27. ↑ "Rabbits, Hares and Pikas. Status Survey and Conservation Action Plan". pp. 61–94. http://wildlife1.wildlifeinformation.org/s/00Ref/BooksContents/b605.htm. 
  28. ↑ 28.0 28.1 De Grouchy J (1987). "Chromosome phylogenies of man, great apes, and Old World monkeys". Genetica 73 (1-2): 37–52. PMID 3333352. 
  29. ↑ Houck ML, Kumamoto AT, Gallagher DS, Benirschke K (2001). "Comparative cytogenetics of the African elephant (Loxodonta africana) and Asiatic elephant (Elephas maximus)". Cytogenet. Cell Genet. 93 (3-4): 249–52. doi:10.1159/000056992. PMID 11528120. 
  30. ↑ Wayne RK, Ostrander EA (1999). "Origin, genetic diversity, and genome structure of the domestic dog". Bioessays 21 (3): 247–57. doi:10.1002/(SICI)1521-1878(199903)21:3 (inactive 2009-03-11). PMID 10333734. 
  31. ↑ Burt DW (2002). "Origin and evolution of avian microchromosomes". Cytogenet. Genome Res. 96 (1-4): 97–112. doi:10.1159/000063018. PMID 12438785. 
  32. ↑ Ciudad J, Cid E, Velasco A, Lara JM, Aijón J, Orfao A (2002). "Flow cytometry measurement of the DNA contents of G0/G1 diploid cells from three different teleost fish species". Cytometry 48 (1): 20–5. doi:10.1002/cyto.10100. PMID 12116377. 
  33. ↑ Yasukochi Y, Ashakumary LA, Baba K, Yoshido A, Sahara K (2006). "A second-generation integrated map of the silkworm reveals synteny and conserved gene order between lepidopteran insects". Genetics 173 (3): 1319–28. doi:10.1534/genetics.106.055541. PMID 16547103. 
  34. ↑ Itoh, Masahiro; Tatsuro Ikeuchi, Hachiro Shimba, Michiko Mori, Motomichi Sasaki, Sajiro Makino (1969). "A COMPARATIVE KARYOTYPE STUDY IN FOURTEEN SPECIES OF BIRDS". The Japanese journal of genetics 44 (3): 163–170. doi:10.1266/jjg.44.163. ISSN 1880-5787. http://www.journalarchive.jst.go.jp/english/jnlabstract_en.php?cdjournal=ggs1921&cdvol=44&noissue=3&startpage=163. Retrieved 2009-10-14. 
  35. ↑ Smith J, Burt DW (1998). "Parameters of the chicken genome (Gallus gallus)". Anim. Genet. 29 (4): 290–4. doi:10.1046/j.1365-2052.1998.00334.x. PMID 9745667. 
  36. ↑ Sakamura, T. (1918), Kurze Mitteilung uber die Chromosomenzahlen und die Verwandtschaftsverhaltnisse der Triticum-Arten. Bot. Mag., 32: 151-154.
  37. ↑ Charlebois R.L. (ed) 1999. Organization of the prokaryote genome. ASM Press, Washington DC.
  38. ↑ Komaki K, Ishikawa H (March 2000). "Genomic copy number of intracellular bacterial symbionts of aphids varies in response to developmental stage and morph of their host". Insect Biochem. Mol. Biol. 30 (3): 253–8. doi:10.1016/S0965-1748(99)00125-3. PMID 10732993. 
  39. ↑ Mendell JE, Clements KD, Choat JH, Angert ER (May 2008). "Extreme polyploidy in a large bacterium". Proc. Natl. Acad. Sci. U.S.A. 105 (18): 6730–4. doi:10.1073/pnas.0707522105. PMID 18445653. PMC 2373351. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=18445653. 
  40. ↑ White, M. J. D. (1973). The chromosomes (6th ed.). London: Chapman and Hall, distributed by Halsted Press, New York. pp. 28. ISBN 0-412-11930-7. 
  41. ↑ von Winiwarter H (1912). "Études sur la spermatogenese humaine". Arch. Biologie 27 (93): 147–9. 
  42. ↑ Painter TS (1922). "The spermatogenesis of man". Anat. Res. 23: 129. 
  43. ↑ Painter TS (1923). "Studies in mammalian spermatogenesis II. The spermatogenesis of man". J. Exp. Zoology 37: 291–336. doi:10.1002/jez.1400370303. 
  44. ↑ Tjio JH, Levan A (1956). "The chromosome number of man". Hereditas 42: 1–6. doi:10.1111/j.1601-5223.1956.tb03010.x. 
  45. ↑ Hsu T.C. Human and mammalian cytogenetics: a historical perspective. Springer-Verlag, N.Y. p10: "It's amazing that he [Painter] even came close!"
  46. ↑ Miller, Kenneth R. (2000). "9-3". Biology (5th ed.). Upper Saddle River, New Jersey: Prentice Hall. pp. 194–5. ISBN 0-13-436265-9. 
  47. ↑ European Chromosome 11 Network
  48. ↑ ORNL.gov, Exploring Genes & Genetic Disorders
  49. ↑ Vega.sanger.ad.uk, all data in this table was derived from this database, November 11, 2008.
  50. ↑ Sequenced percentages are based on fraction of euchromatin portion, as the Human Genome Project goals called for determination of only the euchromatic portion of the genome. Telomeres, centromeres, and other heterochromatic regions have been left undetermined, as have a small number of unclonable gaps. See http://www.ncbi.nlm.nih.gov/genome/seq/ for more information on the Human Genome Project.

External links

Genetics: chromosomes
General
Classification
Autosome · Sex chromosome · Microchromosome
Evolution
Chromosomal inversion · Chromosomal translocation · Polyploidy · Paleopolyploidy
Structure

Nucleosome

Telomere: Telomere-binding protein (TINF2)

Chromatid

Chromatin
Euchromatin · Heterochromatin
H1 · H2A · H2B · H3 · H4
A · B · C1 · C2 · E · F · H · I · J · K · M · N · O · P · Q · T
strc: perx, skel, epit, ctrs, , mito, nucl (chro)