Chromosome

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 nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. Chromosomal DNA encodes most or all of an organism's genetic information; some species also contain plasmids or other extrachromosomal genetic elements.

Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 100,000 to over 3,750,000,000 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. Also, 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 contain two identical copies (called chromatids) 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 unexpectedly 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 loop, 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.

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.

Read more about Chromosome:  History, Prokaryotes, In Eukaryotes, Karyotype, Aberrations

Other articles related to "chromosome, chromosomes":

Contiguous Gene Syndrome
2 or more genes that are located next to each other on a chromosome ... Prader-Willi syndrome occurs when the deletion occurs on the paternal chromosome ... If this deletion occurs on the maternal chromosome, it causes the Angelman syndrome ...
Chromosome Conformation Capture
... Chromosome conformation capture, or 3C, is a high-throughput molecular biology technique used to analyze the organization of chromosomes in a cell's natural state ... structural properties and spatial organization of chromosomes is important for the understanding and evaluation of the regulation of gene expression, DNA ... Chromosome conformation capture has enabled researchers to study the influences of chromosomal activity on the aforementioned cellular mechanisms ...
Meiome - Nondisjunction
... The normal separation of chromosomes in meiosis I or sister chromatids in meiosis II is termed disjunction ... This results in the production of gametes which have either too many or too few of a particular chromosome, and is a common mechanism for trisomy or monosomy ... but not limited to Down Syndrome - trisomy of chromosome 21 Patau Syndrome - trisomy of chromosome 13 Edward Syndrome - trisomy of chromosome 18 ...
Chromosome - Aberrations
... Some chromosome abnormalities do not cause disease in carriers, such as translocations, or chromosomal inversions, although they may lead to a higher chance of ... Abnormal numbers of chromosomes or chromosome sets, called aneuploidy, may be lethal or may give rise to genetic disorders ... Genetic counseling is offered for families that may carry a chromosome rearrangement ...
Supernumerary Chromosome
... Supernumerary chromosome could refer to B chromosome in some animals and plants Small supernumerary marker chromosome (sSMC) in humans ...

Famous quotes containing the word chromosome:

    We become male automatically because of the Y chromosome and the little magic peanut, but if we are to become men we need the help of other men—we need our fathers to model for us and then to anoint us, we need our buddies to share the coming-of-age rituals with us and to let us join the team of men, and we need myths of heroes to inspire us and to show us the way.
    Frank Pittman (20th century)