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Topic: Lyon hypothesis


  
  Hypothesis Encyclopedia   (Site not responding. Last check: 2007-10-14)
A hypothesis (from Greek ὑπόθεσις) consists either of a suggested explanation for a phenomenon or of a reasoned proposal suggesting a possible correlation between multiple phenomena.
In due course, a confirmed hypothesis may become part of a theory or occasionally may grow to become a theory itself.
It is essential in framing an hypothesis that the investigator does not currently know the outcome of a potentially falsifying test or that it remains reasonably under continuing investigation.
www.hallencyclopedia.com /topic/Hypothesis.html   (1259 words)

  
 Newswise Science News | Mary Frances Lyon to Receive Rockefeller’s Pearl Meister Greengard Prize
Lyon, who spent most of her career in the radiobiology unit of the Medical Research Council in the United Kingdom, is honored for her groundbreaking work in mouse genetics.
Trained at Cambridge University, Dr. Lyon's most consequential discovery was the recognition, in 1961, of a fundamental genetic control mechanism called X-chromosome inactivation, also referred to as the Lyon hypothesis, which determined that in mammalian cells with multiple X chromosomes, all but one X chromosome is inactivated during embryogenesis.
Lyon is a member of the Royal Society, the American Academy of Arts and Sciences and the National Academy of Sciences.
www.newswise.com /articles/view/524759/?sc=swtn   (482 words)

  
  Lyon, Mary Frances - Hutchinson encyclopedia article about Lyon, Mary Frances   (Site not responding. Last check: 2007-10-14)
English mouse geneticist who is best known for her theory, now known as the Lyon hypothesis, that one of the X chromosomes (female sex chromosomes) is inactivated during early embryonic development of a female mammal.
Lyon is best known for her discovery of ‘transcriptional inactivation’ of an X chromosome in female cells.
Lyon determined that one of the X chromosomes contracts into a dense object that is transcriptionally inactive.
encyclopedia.farlex.com /Lyon,+Mary+Frances   (337 words)

  
 Dorlands Medical Dictionary
the hypothesis that depression is associated with deficiency of biogenic amines (catecholamines and serotonin), especially norepinephrine, at functionally important receptor sites in the brain and that elation is associated with excess of such amines.
the hypothesis that diabetes mellitus is due to disordered function of the pancreatic islets.
a hypothesis explaining atherogenesis as initiating with some injury to the endothelial cells lining the artery walls, which causes a variety of forms of endothelial dysfunction and leads to abnormal cellular interactions and initiation and progression of atherogenesis.
www.mercksource.com /pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_h_23zPzhtm   (3582 words)

  
 Does Reputation Management Reap Rewards? A Path Analysis of Corporate Reputation Advertising's Impacts on Brand ...
In contrast with the peripheral-cue hypothesis, Lord, Lee and Sauer42 proposed the combined-influence hypothesis.
Hypothesis 5 states: The attitude toward the brand ad will be shown to exert a direct influence on purchase intention independent of the level of the involvement The path coefficients between the attitude toward the brand and purchase intention are.274 under high involvement and.401 under low involvement (See Figure 6 and Figure 8).
Hypothesis 6 states: The attitude toward the brand ad will be shown to exert a direct influence on attitude toward the brand independent of the level of the involvement.
www.scripps.ohiou.edu /wjmcr/vol04/4-1a-b.htm   (6391 words)

  
 March of Dimes awards $250,000 prize to pioneering scientist
"Dr. Lyon's recognition in 1961 of X-chromosome inactivation, which is still referred to as 'Lyonization,' was one of the first great insights into genetic control mechanisms of the 20th century," said Dr. Jennifer L. Howse, president of the March of Dimes.
Lyon's groundbreaking hypothesis explained that, very early in embryonic development, females compensate for the double dose of X chromosomes by randomly switching off one of the X chromosomes in each cell.
Lyon also suggested that the inactive X is reactivated in female egg cells and that, during the early cell division that follows conception, the process begins all over again in the next generation.
www.eurekalert.org /pub_releases/2004-05/modb-mod042304.php   (855 words)

  
 Lyon hypothesis - Wikipedia, the free encyclopedia
The Lyon hypothesis states that in cells with multiple X chromosomes, all but one is inactivated during mammalian embryogenesis.
Many of these genes are dominant genes covering for defective recessive alleles on the active X chromosome to cover such sex-linked disorders as haemophilia and color blindness.
The hypothesis was first stated by Mary F. Lyon in 1961 while she was studying the genetic consequences of radiation exposure, and therefore bears her name.
en.wikipedia.org /wiki/Lyon_hypothesis   (241 words)

  
 [No title]   (Site not responding. Last check: 2007-10-14)
Mary Frances Lyon put forward early in 1961 a disarmingly simple yet elegant hypothesis regarding the random inactivation of one of the two X-chromosomes carried by female mammalian cells.
The Lyon Hypothesis was put forward as a means of achieving this dosage compensation for the genes encoded on the X-chromosome.
In a concise one-page paper (Nature 190: 372, 1961), Lyon argued that this balance was brought about by the random inactivation of either the paternally or maternally inherited X-chromosome in each female cell and that this inactivation occurred early in embryonic development.
www.wolffund.org.il /full.asp?id=99   (225 words)

  
 Mary F. Lyon Summary
In 1962, Lyon proposed the Lyon Hypothesis (now considered as the Lyon Principle) to explain why the phenotypic effect of the X chromosome is the same in the mammalian female that has two X chromosomes, as it is in the male that has only one X chromosome.
The hypothesis proposed that one of the two female X chromosomes is selected at random and inactivated early in embryonic development.
Currently, the Mary Lyon Centre of Excellence in the study of new mouse models of human disease is being established in Harwell.
www.bookrags.com /Mary_F._Lyon   (564 words)

  
 Mammalian Dosage Compensation   (Site not responding. Last check: 2007-10-14)
She made use of her knowledge of mouse coat color mutants to formulate a hypothesis that now bears her name.
If the Lyon hypothesis is correct, then females that are heterozygotes should be mosaics: some of their cells should be G6PD-a and others G6PD-b, but no single cell should carry both the a and b forms.
All together, the evidence that was presented at first seemed to strongly suggest that Lyon's hypothesis was correct.
mbclserver.rutgers.edu /~sofer/genetics/Week10/Lecture12-1.html   (1733 words)

  
 THE FUNCTION OF DELAYED PLUMAGE MATURATION IN MALE BLACK-HEADED GROSBEAKS   (Site not responding. Last check: 2007-10-14)
A third hypothesis is that delayed plumage maturation is an adaptation to the winter rather than the breeding environment (the winter-ad- aptation hypothesis; Rohwer et al.
Predictions 3 and 6.--Given the two strategies for reproduction by yearling males proposed by the female-mimicry hypothesis, subadult males are predicted to establish territories both among adult males in high-quality habitat, with mostly adult males as neighbors, and peripheral to adult males in marginal habitat, with mostly other subadult males as neighbors.
Recent- ly, Lyon and Montgomerie (1986) proposed that the primary role of subadult plumage was to signal subordinance and reduce aggression from adult males.
elibrary.unm.edu /sora/Auk/v105n01/p0001-p0010.html   (9350 words)

  
 Lyon (disambiguation) - Wikipedia, the free encyclopedia
Lyon, France (often known as Lyons in English)
Lyon Court, the institution that regulates heraldry in Scotland
Robert Lyon (duel), last Canadian killed in a duel
en.wikipedia.org /wiki/Lyon_(disambiguation)   (129 words)

  
 Human Genetics - Chromosomal Inheritance 2
Dosage compensation was explained by the discoveries of Mary Lyon.
The Lyon hypothesis states that during early development, about the 100 cell stage in humans, one of the X chromosomes in a female gets turned off and this is maintained in all descendant cells of the clone.
In 1948, before the discoveries of Lyon, Barr and Bertram found that in the interphase nucleus of female cat neurons there were a significant number of cells that had one "darkly staining body" lying along the edge of the nucleus, but they never found a "darkly staining body" in the neurons of male cats.
www.uic.edu /classes/bms/bms655/lesson10.html   (2082 words)

  
 Transcriptional Regulation of an Entire Chromosome: Dosage Compensation
One of the earliest analyses of X chromosome inactivation was performed by Mary Lyon (1961), who observed coat color patterns in mice.
But if a female mouse is heterozygous for a pigmentation gene on the X chromosome, a different result is seen: patches of one parental color alternate with patches of the other parental color (Figure 5.23).
The Lyon hypothesis of X chromosome inactivation provides an excellent account of differential gene inactivation at the level of transcription.
www.ncbi.nlm.nih.gov /books/bv.fcgi?rid=dbio.section.795   (982 words)

  
 [No title]
The hypothesis that an asteroid or comet impact induced the mass extinction at the KT boundary was first proposed in 1980 by a team from the University of California at Berkeley led by Nobel price laureate physicist Luis Alvarez and his geologist son Walter.
Very controversial at first because of its catastrophic aspect, this hypothesis was confirmed in the early 1990's when scientists realized that the impact structure, which lay buried under approximately 1 km of Yucatan platform sediments was in fact the long-sought KT boundary crater predicted by the Alvarez hypothesis.
The Snowball Earth hypothesis proposes that during several profoundly cold periods of Earth's history that occurred from 750 to 600 million years ago, the ocean was covered by a thick sheet of ice.
www.lyon.edu /projects/marsbugs/2001/20011210.txt   (4594 words)

  
 Obstetric care of the affected carrier of hemophilia B -- Seeds et al. 62 (3): 23 -- Obstetrics & Gynecology   (Site not responding. Last check: 2007-10-14)
Hemophilia B (factor IX deficiency) is an X-linked recessive clotting disorder similar to hemophilia A. In both diseases, phenotypic expression of the disorder may occur in significant numbers of heterozygous carriers.
This is presumably due to random inactivation of one of the two X chromosomes of the female carrier as described by the Lyon hypothesis.
The Lyon hypothesis is discussed in detail, and recommendations are made for the care of the clotting factor-deficient gravid woman.
www.greenjournal.org /cgi/content/abstract/62/3/23s   (174 words)

  
 The Rockefeller University - Pearl Meister Greengard Prize awarded to British geneticist Mary Lyon
Lyon, a British geneticist, was recognized for her pioneering work in the field of mouse genetics.
The phenomenon involves the random silencing of one of the two X chromosomes in female mammalian cells during the formation of the embryo.
Lyon headed the genetics division and later the radiobiology unit.
www.rockefeller.edu /benchmarks/benchmarks_121506_d.php   (596 words)

  
 Lyon
Lyon's Restaurant in Grass Valley will be closed for business for a few weeks, but will reopen soon, according to the husband of the woman who owns the building and property.
LYON: Coach Gerard Houllier said that Olympique Lyon will have to learn play without inspirational playmaker Juninho after they qualified for the quarter-finals of the Champions League on Wednesday.
Lyon County senior centers are participating in a nationwide project to raise funds for their Meals on Wheels program.
lyon-in-english.com   (345 words)

  
 Magnetic and Nutritional Therapy
His study supported the hypothesis that a lack of proper oxygen levels in our body destroys the cells, and reduces or eliminates proper cellular regeneration.
Most of us are prone to eat highly processed foods, yeast containing foods, fermented foods such as cheese, and a lot of meats, live a stressful life and sleep to regenerate our bodies with only the depleted magnetic field from the earth.
A Lyon Legacy Magnetic Mattress Pad will enhance the activity and value of the Steps 1 and 2 which are described here.
www.lyonlegacy.com /started.asp?4854   (941 words)

  
 Mary Frances Lyon (www.whonamedit.com)
Hypothesis stating that only one of the two X-chromosomes is genetically active in female cells.
Mary Frances Lyon graduated B.A. from Cambridge University in 1946 and obtained her ScD from the same university in 1948.
Mary Frances Lyon is a Fellow of the Royal Society, a Foreign Associate of the US National Academy of Sciences, and a Foreign Honorary Member of the American Academy of Arts and Sciences.
www.whonamedit.com /doctor.cfm/2472.html   (361 words)

  
 Silence of the Xs - X chromosome inactivation Science News - Find Articles
Building on those data as well as her own work on mice with mottled coats, Mary F. Lyon of the Medical Research Council's Mammalian Genetics Unit in Harwell, England, proposed in 1960 the idea of X inactivation, with the shutoff chromosome becoming the Barr body.
While some critics challenged Lyon's hypothesis, it quickly garnered enough support that X inactivation was called--and still is, by some scientists--Lyonization.
Lyon suggested, for example, that females wouldn't inactivate an X chromosome gene if it had a counterpart on the Y chromosome.
findarticles.com /p/articles/mi_m1200/is_6_158/ai_64697776   (900 words)

  
 RHEJbio4241   (Site not responding. Last check: 2007-10-14)
Due to the Work of Mary Lyon, many advances in molecular genetics have been possible such as the use of transgenic animals as a research tool.
The questions raised by Ohno and Hauschka encouraged Mary Lyon to organize her own research to investigate these issues.
The findings became known as the "Lyon Hypothesis", and were the basis for a 1963 study on humans that demonstrated the X-chromosome inactivation.
www.mun.ca /biology/scarr/4241/RHEJbio4241.html   (724 words)

  
 Veltkamp
Hypothesis pGivesBound : Zpos (vNum b) = Zpower_nat radix p.
Hypothesis pDef: (Closest b radix (x*((powerRZ radix s)+1))%R p).
Hypothesis xPos: (0 < x)%R. Hypothesis Np: Fnormal radix b p.
lipforge.ens-lyon.fr /www/pff/Veltkamp.html   (1294 words)

  
 2nd international conference on X-Inactivation
Mary Lyon proposed the random inactivation of one female X chromosome in 1961 to explain the mottled phenotype of female mice heterozygous for coat color genes.
The Lyon hypothesis also accounted for the findings that one copy of the X chromosome in female cells was highly condensed, and that mice with only one copy of the X chromosome developed as fertile females.
Epigenetics is the study of reversible heritable changes in gene function that occur without a change in the sequence of nuclear DNA.
www.x-inactivation.com /science.htm   (482 words)

  
 XXX Chromosome   (Site not responding. Last check: 2007-10-14)
In contrast, the X is one of the largest chromosomes and contains hundreds of genes, most of which have nothing to do with sex determination.
Lyon hypothesis (X-inactivation): The normal female has two loci for every X-linked gene, as compared with the male's single locus.
However, according to the Lyon hypothesis, one of the two X chromosomes in each somatic cell of the female is genetically inactivated early in the life of the embryo.
www.newton.dep.anl.gov /askasci/mole00/mole00204.htm   (541 words)

  
 Sex Determination
A British geneticist, Mary Lyon, postulated that the Barr Body was in fact, an inactive X chromosome; this has become known as the inactive-X hypothesis or the Lyon hypothesis (See pgs 227-229).
According to this hypothesis, females are mosaic for genes on the X chromosome.
However, a hypothesis of maternal dominance has been proposed which states that women who are more dominant are more likely to conceive sons.
www.washburn.edu /faculty/twolf/sexdet~1.htm   (5240 words)

  
 eMedicine - Hypophosphatemic Rickets : Article Excerpt by: Karl S Roth, MD
Females generally had markedly less bone disease than males, suggesting the random inactivation of the affected X chromosome in females, as might be expected from the Lyon hypothesis.
This recently advanced hypothesis is based upon observations in both affected humans and a murine model but remains to be widely tested.
The pathogenesis of this disorder is clear; phosphate wasting at the proximal tubule level is the basis of the affected individual's inability to establish normal ossification.
www.emedicine.com /ped/byname/hypophosphatemic-rickets.htm   (589 words)

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