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Topic: X chromosome

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	Chromosome - MSN Encarta
		In the cells of most organisms that reproduce sexually, chromosomes occur in pairs: One chromosome is inherited from the female parent, and one is inherited from the male parent.
		Both males and females inherit one sex chromosome from the mother (always an X chromosome) and one sex chromosome from the father (an X in female offspring and a Y in male offspring).
		In males, which carry an X and a Y chromosome, some genes found on the X chromosome may be missing on the Y chromosome.
	encarta.msn.com /encnet/refpages/RefArticle.aspx?refid=761566230 (960 words)

	X chromosome Information Center - x chromosome and y chromosome
		Early in embryonic development picture of the x chromosome in females, one of the two X chromosomes is randomly and permanently inactivated in somatic cells (cells other than egg and sperm cells).
		Chromosomal conditions involving the sex chromosomes often affect sex determination (whether a person has the sexual x chromosome disorders characteristics of a male or a female), sexual development, x chromosome abnorality genetic testing x chromosome and the ability to have children (fertility).
		Recessive genes on the X chromosome that cause serious diseases are usually passed fragile x chromosome carrier from female carriers to their sons and daughters.
	www.scipeeps.com /Sci-Biochemistry_Topics_U_-_Z/X_chromosome.html (1150 words)

	X Chromosome
		The X chromosome is one of the two sex chromosomes that are found in humans, the other being the Y chromosome.
		During the early stages of the embryonic development of a female, one of the two x chromosomes is permanently (but randomly) shut down or turned off in the somatic cells.
		This process of turning off the extra X chromosome is performed by the body to make sure that females, along with males, will only have one working copy of the X chromosome in their cells.
	www.iscid.org /encyclopedia/X_Chromosome (281 words)

	Pharyngula::Evolution of the X chromosome (Site not responding. Last check: 2007-10-09)
		X and Y were initially homomorphic chromosomes, or identical in appearance, with the same arrangement of genes.
		The X chromosome is special—males only have one copy (we should be dead, victims of an underdose!) and females have twice as many copies as we males do (they should be dead of an overdose, or have some syndrome named after them!).
		The levels of expression of the genes on the X chromosome are calibrated to maintain parity between males and females.
	pharyngula.org /index/weblog/comments/evolution_of_the_x_chromosome (3465 words)

	X chromosome - Genetics Home Reference
		The X chromosome is one of the two sex chromosomes in humans (the other is the Y chromosome).
		Genes on the X chromosome are among the estimated 20,000 to 25,000 total genes in the human genome.
		Chromosomal conditions involving the sex chromosomes often affect sex determination (whether a person has the sexual characteristics of a male or a female), sexual development, and the ability to have children (fertility).
	ghr.nlm.nih.gov /chromosome=X (962 words)

	X chromosome - Wikipedia, the free encyclopedia
		The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals (the other is the Y chromosome).
		Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in nearly all somatic cells (cells other than egg and sperm cells).
		Recessive genes on the X chromosome that cause serious diseases are usually passed from female carriers to their ill sons and carrier daughters.
	en.wikipedia.org /wiki/X_chromosome (1293 words)

	genome.gov \| 2005 Release: Studies Expand Understanding of X Chromosome
		Interestingly, almost 10 percent of the genes on the X chromosome are part of a somewhat mysterious family of "cancer-testis antigens," which are normally expressed in the testis but also appear in certain cancers, making them possible targets for immunotherapy.
		The X chromosome's gene density is among the lowest for the human chromosomes that have been analyzed to date.
		Researchers say this may reflect a low density of genes on the ancestral chromosome that gave rise to the X chromosome, or it may indicate that genes coding for key proteins that are required in double dose were transferred from the X chromosome to other chromosomes during the course of mammalian evolution.
	www.genome.gov /13514331 (1115 words)

	Fragile X Syndrome
		Fragile X syndrome is a form of mental retardation caused by a mutated gene on the X chromosome.
		Fragile X syndrome is caused by a mutation in the FMR-1 (Fragile X Mental Retardation) gene, located on the X chromosome.
		The X chromosome is one of two chromosomes that determine an individual's sex.
	www.hmc.psu.edu /childrens/healthinfo/f/fragilex.htm (1103 words)

	Whitehead Institute - Masculinization of the X Chromosome
		This finding is yet another chapter in the 300 million year story of the X and the Y chromosomes, adds Page whose research is unfolding, chapter by chapter, the odyssey of the sex chromosomes that began their lives as autosomes (or non-sex chromosomes) but have since become specialized.
		"The X chromosome is one of the most intensely studied chromosomes, and the X-linked mode of inheritance is a textbook classic—it is one of the three modes of inheritance that we study in medical genetics," says Page.
		The mother, who has a defective gene on one of her two X chromosomes, is protected against the disease because women have two copies of the X, and her normal X makes up for the defective one.
	www.wi.mit.edu /news/archives/2001/el_0329a.html (826 words)

	BBC NEWS \| Science/Nature \| Female chromosome has X factor
		The X chromosome - one of 24 distinct chromosomes found in human cells - is much larger than the relatively puny Y, containing 1,098 genes to the Y's 78.
		Tortoiseshell cats - which are nearly always female - have a gene for one colour on one of their X chromosomes and a gene for another colour on the other X chromosome; and these are expressed in a jumble on the animals' coats, leading to the multicoloured patterning.
		But this leaves males vulnerable to any problems lurking on the X. "Diseases on the X chromosome are usually expressed in males because they don't have a compensating copy of the gene on the second chromosome," said Dr Ross.
	news.bbc.co.uk /1/hi/sci/tech/4355355.stm (870 words)

	LiveScience.com - X Chromosome Key to Differences in Men and Women
		Chromosomes are the threadlike packages of genes and other DNA found in cells of the body.
		People have 24 kinds, numbered 1 through 22 plus the X chromosome and its runty partner, the Y. Women carry two copies of the X chromosome, one inherited from each parent, while men have one X plus one Y chromosome.
		The work raises the possibility that varying activity of genes on the X chromosome can account for not only some differences between the sexes, but also between women, she said.
	www.livescience.com /humanbiology/ap_050316_chromosomes.html (640 words)

	X chromosome
		The Y chromosome is shorter than the X. Genes on these chromosomes determine a person's sex.
		Genes carried on the X chromosome produce the phenomenon of sex linkage.
		Early in the development of a female embryo, one of the X chromosomes becomes condensed so that most of its genes are inactivated.
	www.tiscali.co.uk /reference/encyclopaedia/hutchinson/m0008138.html (380 words)

	Fragile X and company: Finding the right diagnosis -- Subramony et al. 65 (2): E3 -- Neurology
		on the X chromosome that is inherited from the mother.
		Inheritance of fragile X and fragile X tremor-ataxia syndrome (FXTAS).
		The turquoise box in the X chromosome in the maternal grandfather and the mother represent a CGG expansion in the premutation range.
	www.neurology.org /cgi/content/full/65/2/E3 (1193 words)

	Record: Sequencing of X chromosome helps treat genetic disorders
		The X chromosome, by contrast, is sized much closer to the other human chromosomes not involved in sex determination, which are collectively known as autosomes.
		This baring of mutation's effects first led scientists to associate genes with chromosomes in 1910, when a scientist found that a mutation that gives fruit flies white eyes shows up disproportionately in male fruit flies and is linked to inheritance of the X chromosome.
		The X chromosome genome sequence has already allowed researchers to isolate more than 40 genes involved in medical conditions and disorders, which improve their ability to diagnose the disorders and potentially open up new avenues for development of treatments.
	record.wustl.edu /news/page/normal/4984.html (615 words)

	Triple X syndrome - Genetics Home Reference
		Triple X syndrome, also called trisomy X or 47,XXX, is characterized by the presence of one extra X chromosome in each of a female's cells.
		Triple X syndrome is a chromosomal condition related to the X chromosome.
		Two of the 46 chromosomes are sex chromosomes, called X and Y. Females have two X chromosomes (46,XX), and males have one X chromosome and one Y chromosome (46,XY).
	ghr.nlm.nih.gov /condition=triplexsyndrome (663 words)

	washingtonpost.com: Human X Chromosome Coded
		She was slow to reveal her secrets, but the X chromosome has now bared it all.
		Like other chromosomes, X and Y are tangled skeins of DNA that bear genes, the operating instructions inside cells that direct the development and maintenance of the body.
		Although a disease's linkage to the X can be obvious by the pattern of unaffected mothers giving birth to affected sons, the newly completed sequence will speed discovery of the specific genes involved and the development of novel therapies, scientists said.
	www.washingtonpost.com /ac2/wp-dyn/A41919-2005Mar16?language=printer (865 words)

	Home \| aHealthyme.com
		Fragile X syndrome is caused by a mutation in the FMR-1 gene, located on the X chromosome.
		Fragile X syndrome inherited in an X-linked dominant manner (characters are transmitted by genes on the X chromosome).
		When a man carries a premutation on his X chromosome, it tends to be stable and usually will not expand if he passes it on to his daughters (he passes his Y chromosome to his sons).
	www.ahealthyme.com /article/gale/100084591 (1847 words)

	BioMed Central \| Full text \| Abnormal X : autosome ratio, but normal X chromosome inactivation in human triploid ...
		X chromosome inactivation (XCI) is that aspect of mammalian dosage compensation that brings about equivalence of X-linked gene expression between females and males by inactivating one of the two X chromosomes (Xi) in normal female cells, leaving them with a single active X (Xa) as in male cells.
		In the same period, the proportion of cells with three X chromosomes dropped from 85% to 70% in the first experiment, and from 90% to 84% in the second (cell counts shown in Table 1).
		These changes in the numbers of X chromosomes are not statistically significant and they are considerably less than the decrease in the proportion of cells with two inactive X's.
	www.biomedcentral.com /1471-2156/7/41 (4713 words)

	Genomic Sequencing & Gene Identification Group
		The Integrated X Chromosome Database (IXDB) was established in 1996 and is maintained since than.
		In addition, we are involved in sequencing projects of parts of chromosome 2 and 6 of mouse, the MHC of the rat (RT1), and parts of the rhesus MHC.
		Projects to contribute to the sequencing of chimpanzee chromosomes X and Y are initiated, which special emphasis to Xq28 and regions associated with mental retardation.
	www.mpimg-berlin-dahlem.mpg.de /~xteam (362 words)

	Sex - - science news articles online technology magazine articles Sex (Site not responding. Last check: 2007-10-09)
		Meanwhile, the gene-rich X is the most intensely studied of the 23 chromosomes, largely because of its role in rendering men vulnerable to an estimated 300 genetic diseases and disorders associated with those mutations—from color blindness to muscular dystrophy to more than 200 brain disorders.
		While this genetic parcel would boost the son's brilliance, he could pass that X chromosome only to a daughter, where it could be diluted by the maternally derived X. The daughter, in turn, could pass on only a broken-up and remixed version to the fourth generation, due, again, to the recombination that occurs during meiosis.
		By comparing the cognitive social skills of women with a single X chromosome [Turner's syndrome]—which could be either maternal or paternal in origin—with the skills of normal women, who have an X chromosome from both parents, we were able to show that X-linked imprinted genes could influence sexually dimorphic traits.
	www.discover.com /issues/oct-05/features/sex (1309 words)

	UNSW Embryology- Molecular Development - X Inactivation
		The presence in females of 2 X chromosome raises the issue of gene dosage, in the case of mammals this is regulated by inactivating one of the X chromosomes (see X inactivation notes).
		The pattern of which X chromosome is inactivated in cells appears to be random, generating 50% cells expressing Father X, 50% cells expressing Mother X (mosaic pattern).
		A gene from the region of the human X inactivation centre is expressed exclusively from the inactive X chromosome.
	embryology.med.unsw.edu.au /MolDev/Xinact.htm (659 words)

	X chromosome - Susan's Place Transgender Wiki (Site not responding. Last check: 2007-10-09)
		One of the two chromosomes appears to be inactivated (Lyonization) into a Barr body, and it was previously assumed that only one copy is actively used.
		Many diseases are due to mutations on the X chromosome.
		Moreover, they inherit in a characteristic manner: fathers do not transmit them to their sons, but their daughters are carriers as they inherit their father's X chromosome, and their sons have a 50% chance of inheriting that X chromosome.
	wiki.susans.org /index.php/X_chromosome (905 words)

	\|\| DukeMedNews \|\| X Chromosome Variation May Explain Differences Among Women, Between Sexes
		Originally, scientists had assumed that the inactivation process resulted in complete silencing of the genes on the second X chromosome, Willard said, in order to leave both sexes with the same activity level, or dosage, of the genes encoded by the X chromosome.
		However, the large number of genes that escape inactivation and their concentration in certain portions of the X chromosome has immediate implications for counseling the one in every 650 individuals born with X chromosome abnormalities, Willard said.
		The incomplete nature of X inactivation, demonstrated in the new study, means that at least 15 percent of the X-linked genes, and their protein products, are present at characteristically higher, and often variable, levels in females compared to males.
	www.dukemednews.org /news/article.php?id=8450 (1024 words)

	Why do sexes differ? Blame it on X factor - Science - MSNBC.com (Site not responding. Last check: 2007-10-09)
		Chromosomes, which are found in the nucleus of every cell, contain genes that determine the characteristics of an individual.
		The X chromosome is also bigger than the Y and because females have two copies, one X chromosome is largely switched off or inactivated.
		The X chromosome is also home to many genes linked to mental retardation and to the largest gene, called DMD, in the human genome.
	www.msnbc.msn.com /id/7209404 (569 words)

	Wired News: Why X Marks the Gender
		"The X chromosome was pivotal in early human genetics because we were able to see clearly how mutations cause disease," said David Bentley, head of human genetics at the Wellcome Trust Sanger Institute and an author of the sequence paper.
		The X chromosome includes the gene that causes Duchenne muscular dystrophy, the largest known gene at 2.2 million base pairs long.
		Queen Victoria was a carrier of hemophilia but did not suffer from the disorder, meaning that she had the gene causing the disease on one of her X chromosomes but not on the other.
	www.wired.com /news/medtech/0,1286,66919,00.html?tw=wn_tophead_5 (880 words)

	Mammalian Genetics-X/imprinting
		There are two active X chromosomes during ovarian development, and certain genes appear to need to be active for normal ovarian function.
		The inactive X chromosome is reactivated in oogonia when meiosis begins during fetal life.
		X chromosome inactivation involves coordinated regulation of a whole chromosome.
	faculty.virginia.edu /mammgenetics/805-2ndX03.html (2441 words)

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