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Topic: Epistasis


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  Epistasis - Wikipedia, the free encyclopedia
Epistasis takes place when the action of one gene is modified by one or more others that assort somewhat independently.
Fitness epistasis (where the affected trait is fitness) is the cause of linkage disequilibrium.
Epistasis and genetic interaction refer to the same phenomenon; however, epistasis is widely used in population genetics and refers especially to the statistical properties of the phenomenon.
en.wikipedia.org /wiki/Epistasis   (536 words)

  
 Stanley C. Spencer -- Chamaecrista fasciculata   (Site not responding. Last check: 2007-10-16)
Epistasis exists when the effect (on fitness, or any phenotypic trait) of a genotype at one locus differs depending on the genotype at a second locus.
This study is concerned with the role of epistasis for fitness in the evolutionary divergence of populations.
In the absence of epistasis, the mean fitness of the F2 and F3 generations should be half way between the mean fitness of the parents and the mean fitness of the F1, i.e.
users.mstar2.net /spencersa/evolutus/poster.html   (2086 words)

  
 Genetic Measurement Theory of Epistatic Effects
Epistasis is defined as the influence of the genotype at one locus on the effect of a mutation at another locus.
In mathematical population genetics, however, epistasis is often represented as a mere noise term in an additive model of gene effects.
It is concluded that non-linearity of the genotype-phenotype map is not sufficient to cause epistasis.
www.cbc.yale.edu /old/cce/papers/epistasis/epistasis.html   (384 words)

  
 Epistasis Blog: February 2005
Epistasis plays an important role in the genetic architecture of common human diseases and can be viewed from two perspectives, biological and statistical, each derived from and leading to different assumptions and research strategies.
Biological epistasis is the result of physical interactions among biomolecules within gene regulatory networks and biochemical pathways in an individual such that the effect of a gene on a phenotype is dependent on one or more other genes.
In contrast, statistical epistasis is defined as deviation from additivity in a mathematical model summarizing the relationship between multilocus genotypes and phenotypic variation in a population.
compgen.blogspot.com /2005_02_01_compgen_archive.html   (1595 words)

  
 Mendelian Genetics
Because the presence of the dominant W allele masks the effects of either the G or g allele, this type of interaction is called dominant epistasis.
Because the action of the dominant D allele masks the genes at the K locus, this interaction is termed dominant suppression epistasis.
Remember that epistasis is the interaction between different genes.
www.ndsu.nodak.edu /instruct/mcclean/plsc431/mendel/mendel6.htm   (849 words)

  
 PCB 4673 About Epistasis
Let's begin by recalling the definition: epistasis is the interaction between alleles at different loci that allows an allele at one locus to alter the effects of alleles at a different locus.
The interesting part is that epistasis can produce almost any type of genotype-phenotype relationship; the frustrating part is that there is no formula or guide to its effects that one can use.
The key to understanding epistasis for our purposes (and, actually, for any purpose) is to recognize that an epistatic effect on a quantitative trait causes a deviation from an additive effect of alleles across loci.
www.bio.fsu.edu /courses/pcb4673/about_epistasis.html   (1092 words)

  
 ECS EPrints Service - Perspective:Sign Epistasis and Genetic Constraint on Evolutionary Trajectories
Epistasis for fitness means that the selective effect of a mutation is conditional on the genetic background in which it appears.
Although epistasis is widely observed in nature, our understanding of its consequences for evolution by natural selection remains incomplete.
Sign epistasis means that the sign of the fitness effect of a mutation is under epistatic control; thus, such a mutation is beneficial on some genetic backgrounds and deleterious on others.
eprints.ecs.soton.ac.uk /11612   (353 words)

  
 BioMed Central | Full text | Compensatory mutations cause excess of antagonistic epistasis in RNA secondary structure ...
Closely related to this geometric approach is the realization that epistasis must be studied with respect to a particular reference sequence [7-11], and that the forms of epistatic interactions change when the reference is changed.
Wilke and Adami [11] proposed that inhomogeneities in the distribution of genotypes give rise to directional epistasis (directional epistasis is the net epistasis averaged over many pairs of mutations) among deleterious mutations, and that the sign of directional epistasis provides information about the density gradient of high-fitness sequences within a cluster.
The correlation between average mutational effects (α) and directional epistasis (β) described by Wilke and Adami [11] implies that whether a reference sequence shows synergistic or antagonistic epistasis depends on whether it lies near the center of a dense cluster of high-fitness sequences in genetic space, or on the fringes of such a cluster.
www.biomedcentral.com /1471-2148/3/3   (6790 words)

  
 Epistasis Blog
Epistasis and the release of genetic variation during long-term selection
Studies like this support Alan Templeton's statement that epistasis will be uncovered when properly investigated (see his chapter in Epistasis and the Evolutionary Process).
This explanation requires negative epistasis, a type of genetic interaction where mutations are more harmful in combination than expected from their separate effects.
compgen.blogspot.com   (2281 words)

  
 Absence of Epistasis for Grain Yield in Elite Maize Hybrids -- Hinze and Lamkey 43 (1): 46 -- Crop Science
Epistasis and its consequences for the evolution of natural populations.
Epistasis in an elite maize hybrid and choice of generation for inbred line development.
Importance of epistasis as the genetic basis of heterosis in an elite rice hybrid.
crop.scijournals.org /cgi/content/full/43/1/46   (3225 words)

  
 Gene Interactions   (Site not responding. Last check: 2007-10-16)
A 9:3:4 phenotypic ratio is a hallmark of recessive epistasis.
The 9: 3 : 4 ratio is indicative of recessive epistasis.
is a hallmark of dominant epistasis I. Dominant epistasis II White wyandotte chickens and white leghorn chickens have predominantly white feathers.
www.park.edu /bhoffman/courses/bi320/recaps/genteractions.htm   (1405 words)

  
 MCDB 2150 -- Lecture 25
Under "Major concepts", the ratio for recessive epistasis is "9:4:3", and not 12:4 as previously shown.
Epistasis in Bombay phenotype: We have already observed an example of epistasis in failure of expression of type A and type B blood groups by individuals with the Bombay phenotype.
This yields the characteristic 9:4:3 phenotypic ratio for recessive epistasis.
www.colorado.edu /MCDB/MCDB2150Fall/notes00/L0025.html   (3707 words)

  
 Evolution - A-Z - Epistasis   (Site not responding. Last check: 2007-10-16)
Epistasis is the interaction between the genes at two or more loci, so that the phenotype differs from what would be expected if the loci were expressed independently.
It is important in population genetics when the fitness effects of a genotype depend on what genotype it is associated with at the other locus.
A good example of epistatic interaction is found in the case of the Papilio memnon butterfly, which is pictured opposite.
www.blackwellpublishing.com /ridley/a-z/Epistasis.asp   (88 words)

  
 Hartl Lab - Daniel Weinreich   (Site not responding. Last check: 2007-10-16)
Traditionally attention has focused on the problem of evolutionary constraint if a population's trajectory across the landscape becomes 'stuck' on a sub-optimal peak, but empirical progress is difficult owing to the very high dimensionality of the landscape.
Sign epistasis also suggested a novel partitioning of the infinite universe of possible fitness landscapes into a finite number of classes that I call fitness rank orderings.
This motivates a general model of protein evolution that integrates both structural and functional demands on the molecule and which explains a variety of diverse observations from the dynamics of protein evolution to the over-dispersed molecular clock
www.oeb.harvard.edu /hartl/lab/people/weinreich.html   (1768 words)

  
 Multipeak Epistasis   (Site not responding. Last check: 2007-10-16)
Epistasis is the interaction among genetic loci in their effects on phenotypes or fitness.
Epistasis can play a special role in the evolutionary process because it can create multiple fitness optima (adaptive peaks) separated by fitness minima (adaptive valleys).
We review the evidence that epistasis is a common phenomenon in natural populations.
darkwing.uoregon.edu /~pphil/pubs/annrev1995.html   (272 words)

  
 Epistasis in Monkeyflowers -- Kelly 171 (4): 1917 -- Genetics
Epistasis in Monkeyflowers -- Kelly 171 (4): 1917 -- Genetics
, J. and C., 1992 Epistasis and the genetic divergence of photoperiodism between populations of the pitcher-plant mosquito, Wyeomyia smithii.
Epistasis and the Evolutionary Process, edited by J. and M. Oxford University Press, Oxford.
www.genetics.org /cgi/content/full/171/4/1917   (7075 words)

  
 Modular epistasis in yeast metabolism - Nature Genetics
Although the implications of epistasis have been studied mostly under the assumption of identical interactions between all mutations, variability in the level and 'sign' (aggravating or buffering; Table 1) of epistasis between different loci could substantially affect (and sometimes even reverse) its evolutionary consequences
The genetic architecture of odor-guided behavior in Drosophila: epistasis and the transcriptome.
You, L.C. and Yin, J. Dependence of epistasis on environment and mutation severity as revealed by in silico mutagenesis of phage T7.
www.nature.com /ng/journal/v37/n1/full/ng1489.html   (4803 words)

  
 Molecular Biology Encyclopedia Article @ NaturalResearch.org   (Site not responding. Last check: 2007-10-16)
The study of "mutants" – organisms which lack one or more functional components with respect to the so-called "wild type" or normal phenotype.
Genetic interactions such as epistasis can often confound simple interpretations of such "knock-out" studies.
Molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material.
www.naturalresearch.org /encyclopedia/Molecular_biology   (1765 words)

  
 Amazon.co.uk: Epistasis and the Evolutionary Process: Books   (Site not responding. Last check: 2007-10-16)
This book will servce as a primer on no-additive evolutionary genetics, integrating the work to date on all levels of evolutionary investigation of the importance of epistasis to the evolutionary process in general.
It has become clear that the effects of genes are rarely independent, and to reach a fuller understanding of the process of evolution, one must consider the issue of complex traits, meaning gene interactions as well as gene-environment interactions.
It includes an historic perspective on this emerging field, an in-depth discussion of terminology, discussions of the effects of epistasis at several different levels of biological organisation (the individual, the population, the metapopulation and the species) and combinations of theoretical and experimental approaches to analyse a single question.
www.amazon.co.uk /exec/obidos/ASIN/0195128060   (680 words)

  
 Modeling Epistasis of Quantitative Trait Loci Using Cockerham's Model -- Kao and Zeng 160 (3): 1243 -- Genetics
for modeling epistasis and defining gene effects in a population.
epistasis is ignored, the accuracy in estimation and power of
Epistasis plot of the four types of epistasis from the data of
www.genetics.org /cgi/content/full/160/3/1243   (4501 words)

  
 Epistasis, Genetic
Prokaryotic Genetics and Gene Expression is a chapter of the MIT Biology Hypertextbook, designed by the Experimental Study Group at Massachusetts Institute of Technology to supplement the course materials of their Introductory Biology course.
The Prokaryotic Genetics and Gene Expression chapter contains a section on prokaryotic genetics; tools for studying prokaryotic genetics and regulation, and biochemical genetics, complementation and epistasis; and another section on the regulation of prokaryotic genes, using a number of examples including the lac, tryptophan and histidine operons, and the lambda phage cycle.
This chapter is aimed at university students beginning their studies in biological sciences, and is designed to serve as an introduction to more advanced courses.
bioresearch.ac.uk /browse/mesh/D004843.html   (196 words)

  
 Epistasis   (Site not responding. Last check: 2007-10-16)
Different genes can interact to control the phenotypic expression of a single trait.
In some cases, a gene at one locus alters the phenotypic expression of a second gene, a condition known as epistasis.
Epistasis = (Epi = upon; stasis = standing) Interaction between two nonallelic genes in which one modifies the phenotypic expression of the other.
www.d.umn.edu /biology/courses/bio1011/epistasis.htm   (73 words)

  
 Model Horse Reference -- Genetic Inheritance Basics
Epistasis refers to the presence of a certain allele or allele combination at one locus, which affects the expression of the genotype at a completely different locus.
The best example of Epistasis in the horse, is the basic determination of Bay, Black and Chestnut colors.
All horses, underneath all other modifying colors and patterning are either Bay, Black or Chestnut.
www.mhref.com /color/genetics/tour/basic5.html   (637 words)

  
 Jan Paredis's Matrix Epistasis Generator   (Site not responding. Last check: 2007-10-16)
By setting off-diagonal entries to non-zero, the degree of epistasis is increased: the more non-zero off-diagonal elements in A, the higher the degree of epistasis.
This procedure is used to produce problems with different degrees of epistasis.
In order to allow for easy experimentation, the bi are chosen such that all components xi of the solution to the system of equations are equal to 1.
www.cs.uwyo.edu /~wspears/gen.paredis.html   (464 words)

  
 epistasis - OneLook Dictionary Search
Tip: Click on the first link on a line below to go directly to a page where "epistasis" is defined.
Epistasis : Drug Discovery and Development [home, info]
Words similar to epistasis: epistases, epistatic, hypostasis, more...
www.onelook.com /?w=epistasis   (172 words)

  
 OUP: Epistasis and the Evolutionary Process: Wolf
"I learned a great deal from Epistasis and the Evolutionary Process, and I congratulate the editors on an excellent choice of authors.Graduate students and other scientists will find the book a very useful smorgrasbord of recent research into theory and facts of epistasis.
The volume does not attempt to resolve the 70 year old controversy about the importance of epistasis and shifting balance.
Instead, it shows that epistasis plays a central role in a much wider and more interesting variety of evolutionary problems than seemed possible even ten years ago" Science
www.oup.co.uk /isbn/0-19-512806-0?view=00   (644 words)

  
 Online Feline Fanciers: The Pigment Parade
When we see a beautiful shimmering white Persian we know that at least one of his parents was white.
The term "epistasis" refers to the fact that the cat's "whiteness" covers up whatever color he may be underneath.
For all you know, that white Persian is genetically a shaded tortoiseshell, or a blue lynx point, or a dilute calico.
home.earthlink.net /~featherland/off/white.html   (2917 words)

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