Chromosome
hideA 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. 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 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.
However, in practice "chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins.
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News tagged with chromosomes
Down Syndrome becoming more prevalent in the U.S.
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(PhysOrg.com) -- A new study, aimed at estimating the prevalence of Down Syndrome in newborns, children and teenagers in 10 areas of the U.S., has found an increase in prevalence of more than 30 percent over ...
Long-term physical activity has an anti-aging effect at the cellular level
Nov 30, 2009 |
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Intensive exercise prevented shortening of telomeres, a protective effect against aging of the cardiovascular system, according to research reported in Circulation: Journal of the American Heart Association.
When is a stem cell really a stem cell?
Nov 24, 2009 |
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(PhysOrg.com) -- Induced pluripotent stem (iPS) cells -- adult cells reprogrammed to look and function like versatile embryonic stem cells -- are of growing interest in medicine. They may provide a way to ...
Longevity tied to genes that preserve tips of chromosomes
Nov 11, 2009 |
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A team led by researchers at Albert Einstein College of Medicine of Yeshiva University has found a clear link between living to 100 and inheriting a hyperactive version of an enzyme that rebuilds telomeres - the tip ends ...
Chromosomes dance and pair up on the nuclear membrane (w/ Video)
Nov 13, 2009 |
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(PhysOrg.com) -- Meiosis - the pairing and recombination of chromosomes, followed by segregation of half to each egg or sperm cell - is a major crossroads in all organisms reproducing sexually. Yet, how the ...
Genome sequence for the domestic horse unveiled
Nov 05, 2009 |
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The whole genome sequence of the domestic horse has been completed by the genome-sequencing center of The Broad Institute of MIT and Harvard, in collaboration with an international team of researchers that ...
Cucumber genome published
Nov 02, 2009 |
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The genome of the cucumber has been sequenced by an international consortium lead by Chinese and U.S. institutions. The annotated genome is published online Nov. 1 by the journal Nature Genetics.
Researchers discover mechanism that prevents two species from reproducing
Oct 26, 2009 |
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Cornell researchers have discovered a genetic mechanism in fruit flies that prevents two closely related species from reproducing, a finding that offers clues to how species evolve.
US trio win Nobel Medicine Prize for research into ageing (Update 3)
Oct 05, 2009 |
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Australian-American researcher Elizabeth Blackburn and Carol Greider and Jack Szostak of the United States won the Nobel Medicine Prize on Monday for identifying a key switch in cellular ageing.
Male sex chromosome losing genes by rapid evolution, study reveals
Jul 17, 2009 |
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Scientists have long suspected that the sex chromosome that only males carry is deteriorating and could disappear entirely within a few million years, but until now, no one has understood the evolutionary ...
Sex Talk Revelations of the Lonely Y Chromosome
Sep 09, 2009 |
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(PhysOrg.com) -- In the week that the University of Leicester celebrates the 25th anniversary of the discovery of DNA fingerprinting (Thursday September 10) new findings from the world-renowned University of Leicester Department ...
Rare mutation dramatically increasing schizophrenia risk
Oct 25, 2009 |
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An international team of researchers led by geneticist Jonathan Sebat, Ph.D., of Cold Spring Harbor Laboratory (CSHL), has identified a mutation on human chromosome 16 that substantially increases risk for schizophrenia.
Genetic conflict in fish led to evolution of new sex chromosomes
Oct 01, 2009 |
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University of Maryland biologists have genetically mapped the sex chromosomes of several species of cichlid (pronounced "sick-lid") fish from Lake Malawi, East Africa, and identified a mechanism by which new ...
Researchers examine mechanisms that help cancer cells proliferate
Sep 01, 2009 |
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A process that limits the number of times a cell divides works much differently than had been thought, opening the door to potential new anticancer therapies, researchers at UT Southwestern Medical Center report in the Aug. ...
After dinosaurs, mammals rise but their genomes get smaller
Jul 27, 2009 |
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(PhysOrg.com) -- Evidence buried in the chromosomes of animals and plants strongly suggests only one group -- mammals -- have seen their genomes shrink after the dinosaurs' extinction. What's more, that trend continues today, ...
