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==Origin==
German ''chromosom''
*[http://en.wikipedia.org/wiki/19th_century 19th Century]
The [[word]] chromosome comes from the [[Greek]] χρῶμα (chroma, [[colour]]) and σῶμα (soma, [[body]]) due to their property of being very strongly stained by particular dyes.
==Definition==
*1: any of the rod-shaped or threadlike [[DNA]]-containing [[structures]] of cellular [[organisms]] that are located in the [[nucleus]] of [http://en.wikipedia.org/wiki/Eukaryote eukaryotes], are usually ring-shaped in [http://en.wikipedia.org/wiki/Prokaryotic prokaryotes] (as bacteria), and contain all or most of the genes of the [[organism]]; also : the genetic material of a [[virus]]
==Description==
A '''chromosome''' is an organized [[structure]] of [[DNA]] and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other [http://en.wikipedia.org/wiki/Genetic_sequence nucleotide sequences]. Chromosomes also contain DNA-bound [http://en.wikipedia.org/wiki/Protein proteins], which serve to package the DNA and [[control]] its [[functions]].
Chromosomes vary widely between different [[organisms]]. The [[DNA]] [[molecule]] may be [[circular]] or [[linear]], and can be composed of 100,000 to 10,000,000,000 nucleotides in a long [[chain]]. Typically, [http://en.wikipedia.org/wiki/Eukaryote eukaryotic] cells (cells with [[nuclei]]) have large linear chromosomes and [http://en.wikipedia.org/wiki/Prokaryotic prokaryotic] cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Also, cells may contain more than one type of chromosome; for example, [http://en.wikipedia.org/wiki/Mitochondria 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 [http://en.wikipedia.org/wiki/Chromatin chromatin]. This allows the very long [[DNA]] [[molecules]] to fit into the cell [[nucleus]]. The structure of chromosomes and chromatin varies through the [http://en.wikipedia.org/wiki/Cell_cycle 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 [http://en.wikipedia.org/wiki/S_phase synthesis phase]) contain two copies joined by a [http://en.wikipedia.org/wiki/Centromere centromere].
Compaction of the duplicated chromosomes during [http://en.wikipedia.org/wiki/Mitosis 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 [http://en.wikipedia.org/wiki/Mitotic_catastrophe mitotic catastrophe] and die, or it may unexpectedly evade [http://en.wikipedia.org/wiki/Apoptosis apoptosis] leading to the progression of cancer.
In [[practice]] "chromosome" is a rather loosely defined term. In prokaryotes and [[viruses]], the term [http://en.wikipedia.org/wiki/Genophore 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 [http://en.wikipedia.org/wiki/Plasmid 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 [http://en.wikipedia.org/wiki/RNA RNA] molecules are short linear or circular genophores that often lack structural proteins.[http://en.wikipedia.org/wiki/Chromosome]
[[Category: Biology]]
==Origin==
German ''chromosom''
*[http://en.wikipedia.org/wiki/19th_century 19th Century]
The [[word]] chromosome comes from the [[Greek]] χρῶμα (chroma, [[colour]]) and σῶμα (soma, [[body]]) due to their property of being very strongly stained by particular dyes.
==Definition==
*1: any of the rod-shaped or threadlike [[DNA]]-containing [[structures]] of cellular [[organisms]] that are located in the [[nucleus]] of [http://en.wikipedia.org/wiki/Eukaryote eukaryotes], are usually ring-shaped in [http://en.wikipedia.org/wiki/Prokaryotic prokaryotes] (as bacteria), and contain all or most of the genes of the [[organism]]; also : the genetic material of a [[virus]]
==Description==
A '''chromosome''' is an organized [[structure]] of [[DNA]] and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other [http://en.wikipedia.org/wiki/Genetic_sequence nucleotide sequences]. Chromosomes also contain DNA-bound [http://en.wikipedia.org/wiki/Protein proteins], which serve to package the DNA and [[control]] its [[functions]].
Chromosomes vary widely between different [[organisms]]. The [[DNA]] [[molecule]] may be [[circular]] or [[linear]], and can be composed of 100,000 to 10,000,000,000 nucleotides in a long [[chain]]. Typically, [http://en.wikipedia.org/wiki/Eukaryote eukaryotic] cells (cells with [[nuclei]]) have large linear chromosomes and [http://en.wikipedia.org/wiki/Prokaryotic prokaryotic] cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Also, cells may contain more than one type of chromosome; for example, [http://en.wikipedia.org/wiki/Mitochondria 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 [http://en.wikipedia.org/wiki/Chromatin chromatin]. This allows the very long [[DNA]] [[molecules]] to fit into the cell [[nucleus]]. The structure of chromosomes and chromatin varies through the [http://en.wikipedia.org/wiki/Cell_cycle 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 [http://en.wikipedia.org/wiki/S_phase synthesis phase]) contain two copies joined by a [http://en.wikipedia.org/wiki/Centromere centromere].
Compaction of the duplicated chromosomes during [http://en.wikipedia.org/wiki/Mitosis 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 [http://en.wikipedia.org/wiki/Mitotic_catastrophe mitotic catastrophe] and die, or it may unexpectedly evade [http://en.wikipedia.org/wiki/Apoptosis apoptosis] leading to the progression of cancer.
In [[practice]] "chromosome" is a rather loosely defined term. In prokaryotes and [[viruses]], the term [http://en.wikipedia.org/wiki/Genophore 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 [http://en.wikipedia.org/wiki/Plasmid 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 [http://en.wikipedia.org/wiki/RNA RNA] molecules are short linear or circular genophores that often lack structural proteins.[http://en.wikipedia.org/wiki/Chromosome]
[[Category: Biology]]
