View source for Clone (cell biology)

[[Image:Clonal expansion and monoclonal versus polyclonal proliferation.PNG|thumb|400px|right|Clonal expansion and monoclonal versus polyclonal proliferation]]
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A '''clone''' is a group of ''identical'' cells that share a ''common ancestry'', meaning are derived from the same mother cell.<sup><ref>[http://www.medterms.com/script/main/art.asp?articlekey=2754 Clone definition - Medical Dictionary definitions of popular medical terms easily defined on MedTerms<!-- Bot generated title -->]</ref></sup>

Clonality implies the state of a cell or a substance being derived from one source or the other. Thus there are terms like ''polyclonal''--derived from '''many''' clones; ''oligoclonal''<sub><ref>[http://medical.merriam-webster.com/medical/oligoclonal oligoclonal - Definition from Merriam-Webster's Medical Dictionary<!-- Bot generated title -->]</ref></sub>--derived from a '''few''' clones; and, ''monoclonal''--derived from '''one''' clone. These terms are most commonly used in context of antibodies or immunocytes.

==Contexts==

This concept of clone assumes importance as all the cells that form a clone share common ancestry with a very important consequence--shared [[genotype]].

# One of the most prominent usage is in describing a clone of [[B cell]]s. The B cells in the body have two important [[phenotypes]] (functional forms)--the antibody secreting, terminally differentiated (that is, they cannot divide further) plasma cells, and the memory and the naive cells, both of which retain their proliferative potential.
# Another important area where one can talk of "clones" of cells is [[neoplasm]]s.<sub><ref>[http://ajp.amjpathol.org/cgi/content/full/162/1/353 Clonal Origin and Expansions in Neoplasms: Biologic and Technical Aspects Must Be Considered Together - Pozo-Garcia et al. 162 (1): 353 - American Journal of Pathology<!-- Bot generated title -->]</ref></sub> Many of the tumors derive from '''[[neoplasm#Clonality|one]]''' (sufficiently) mutated cell, so they are technically a single clone of cells. However, during course of cell division, one of the cells can get mutated further and acquire new characteristics to diverge as a new clone. This is how, in fact, drug resistance could be acquired in many cases.
# All the [[granulosa cells]] in a [[ovarian follicle|Graafian follicle]] are in fact a clone.
# [[Paroxysmal nocturnal hemoglobinuria]] is a disorder of bone marrow cells resulting in shortened life of red blood cells, which is also a result of clonal expansion, i.e., all the altered cells are originally derived from a single cell, which also somewhat compromises the functioning of other "normal" bone marrow cells.<sub><ref>{{cite book
| last =Bunn 
| first =Franklin 
| authorlink = 
| coauthors =Wendell Rosse 
| title =Harrison's PRINCIPLES OF INTERNAL MEDICINE, Sixteenth Edition 
| publisher =The McGraw-Hill Companies, Inc. 
| date =2005 
| location =
| volume =1 
| page =616 
| url = 
| doi = 
| id = 
| isbn =0-07-144746-6 }}</ref></sub>

==Basis of clonal proliferation==

Most of the other cells cannot divide indefinitely as after a few cycles of cell division the cells stop expressing an enzyme [[telomerase]]. The genetic material in form of [[deoxyribonucleic acid|deoxyribonucleic acid (DNA)]] keeps on getting shortened with each cell division, and cells stop dividing when they sense that their DNA is critically shortened. However, this enzyme in "youthful" cells replaces these lost bits ([[nucleotides]]) of DNA thus making almost unlimited cycles of cell division possible. It is believed that the above mentioned tissues have a constitutional elevated expression of telomerase. When ultimately many cells are produced by a single cell, ''clonal expansion'' is said to have taken place.

==Concept of clonal colony==

A somewhat similar concept is that of ''[[clonal colony]]'' (also called a ''genet''), wherein the cells (usually unicellular) also share a common ancestry, but which also requires the products of clonal expansion to reside at "one place", or in close proximity. A clonal colony would be well exemplified by a bacterial culture colony, or the bacterial films that are more likely to be found in vivo (in infected multicellular hosts). Whereas, the cells of clones dealt with here are specialized cells of a multicellular organism (usually vertebrates), and may be residing at quite distant places. For instance, two plasma cells belonging to the same clone could be derived from different memory cells (in turn with shared clonality), and be residing in quite distant locations like the cervical (in the neck) and inguinal (in the groin) [[lymph node|lymph nodes]].

==See also==

* [[Polyclonal antibodies]]
* [[Polyclonal response]]
* [[Clone (B-cell biology)]]

==References==

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[[Category:Cell biology stubs]]
[[Category:Molecular and cellular biology stubs]]
[[Category:cell biology]]
[[Category:immunology]]


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