Gene-environment interaction
Encyclopedia
Gene–environment interaction (or genotype–environment interaction or G×E) is the phenotypic
effect of interactions between genes
and the environment.
Gene–environment interaction is exploited by plant and animal breeders to benefit agriculture. For example, plants can be bred to have tolerance for specific environments, such as high or low water availability. The way that trait expression varies across a range of environments for a given genotype
is called its norm of reaction.
In genetic epidemiology
it is frequently observed that diseases cluster in families, but family members may not inherit disease as such. Often, they inherit sensitivity to the effects of various environmental risk factors
. Individuals may be differently affected by exposure to the same environment in medically significant ways. For example, sunlight exposure has a much stronger influence on skin cancer
risk in fair-skinned humans than in individuals with an inherited tendency to darker skin.
Naive nature versus nurture
debates assume that variation in a given trait is primarily due to either genetic variability
or exposure to environmental experiences. The current scientific view is that neither genetics nor environment are solely responsible for producing individual variation, and that virtually all traits show gene–environment interaction. Evidence of statistical interaction between genetic and environmental risk factors is often used as evidence for the existence of an underlying mechanistic interaction.
, such as human
s, environmental influences may act during either pre- or post-natal development; similarly environmental influences may act before and after hatching to affect development in oviparous animals. Environmental influences in utero
may be as strong and lasting as genetic or post-natal environmental influence. There is increasing study of environmental influences affecting genetic factors directly but nonheritably; see the Epigenetics
article for a detailed discussion.
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
effect of interactions between genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
and the environment.
Gene–environment interaction is exploited by plant and animal breeders to benefit agriculture. For example, plants can be bred to have tolerance for specific environments, such as high or low water availability. The way that trait expression varies across a range of environments for a given genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
is called its norm of reaction.
In genetic epidemiology
Genetic epidemiology
Genetic epidemiology is the study of the role of genetic factors in determining health and disease in families and in populations, and the interplay of such genetic factors with environmental factors...
it is frequently observed that diseases cluster in families, but family members may not inherit disease as such. Often, they inherit sensitivity to the effects of various environmental risk factors
Risk factors
A risk factor is a concept in finance theory such as the CAPM, APT and other theories that use pricing kernels. In these models, the rate of return of an asset is a random variable whose realization in any time period is a linear combination of other random variables plus a disturbance term or...
. Individuals may be differently affected by exposure to the same environment in medically significant ways. For example, sunlight exposure has a much stronger influence on skin cancer
Skin cancer
Skin neoplasms are skin growths with differing causes and varying degrees of malignancy. The three most common malignant skin cancers are basal cell cancer, squamous cell cancer, and melanoma, each of which is named after the type of skin cell from which it arises...
risk in fair-skinned humans than in individuals with an inherited tendency to darker skin.
Naive nature versus nurture
Nature versus nurture
The nature versus nurture debate concerns the relative importance of an individual's innate qualities versus personal experiences The nature versus nurture debate concerns the relative importance of an individual's innate qualities ("nature," i.e. nativism, or innatism) versus personal experiences...
debates assume that variation in a given trait is primarily due to either genetic variability
Genetic variability
Genetic variability is a measure of the tendency of individual genotypes in a population to vary from one another. Variability is different from genetic diversity, which is the amount of variation seen in a particular population. The variability of a trait describes how much that trait tends to...
or exposure to environmental experiences. The current scientific view is that neither genetics nor environment are solely responsible for producing individual variation, and that virtually all traits show gene–environment interaction. Evidence of statistical interaction between genetic and environmental risk factors is often used as evidence for the existence of an underlying mechanistic interaction.
Examples
- A classic example of gene–environment interaction is Tryon's artificial selectionArtificial selectionArtificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
experiment on maze-running ability in rats. Tryon produced a remarkable difference in maze running ability in two selected lines after seven generations of selecting "bright" and "dull" lines by breeding the best and worst maze running rats with others of similar abilities. The difference between these lines was clearly genetic since offspring of the two lines, raised under identical typical lab conditions, performed too differently. This difference disappeared in a single generation, if those rats were raised in an enriched environmentEnvironmental enrichment (neural)Environmental enrichment concerns how the brain is affected by the stimulation of its information processing provided by its surroundings . Brains in richer, more stimulating environments, have increased numbers of synapses, and the dendrite arbors upon which they reside are more complex...
with more objects to explore and more social interaction. This result shows that maze running ability is the product of a gene-by-environment interaction; the genetic effect is only seen under some environmental conditions. - Seven genetically distinct yarrow plants were collected and three cuttings taken from each plant. One cutting of each genotype was planted at low, medium, and high elevations, respectively. When the plants matured, no one genotype grew best at all altitudes, and at each altitude the seven genotypes fared differently. For example, one genotype grew the tallest at the medium elevation but attained only middling height at the other two elevations. The best growers at low and high elevation grew poorly at medium elevation. The medium altitude produced the worst overall results, but still yielded one tall and two medium-tall samples. Altitude had an effect on each genotype, but not to the same degree nor in the same way.
- Phenylketonuria (PKU) is a human genetic conditionGenetic disorderA genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
caused by mutations to a gene coding for a particular liver enzyme. In the absence of this enzyme, an amino acidAmino acidAmino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
known as phenylalanine does not get converted into the next amino acid in a biochemical pathwayMetabolic pathwayIn biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function...
, and therefore too much phenylalanine passes into the blood and other tissues. This disturbs brain developmentNeural developmentNeural development comprises the processes that generate, shape, and reshape the nervous system, from the earliest stages of embryogenesis to the final years of life. The study of neural development aims to describe the cellular basis of brain development and to address the underlying mechanisms...
leading to mental retardationMental retardationMental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
and other problems. PKU affects approximately 1 out of every 15,000 infants in the U.S. However, most affected infants do not grow up impaired because of a standard screening program used in the U.S. and other industrialized societies. Newborns found to have high levels of phenylalanine in their blood can be put on a special, phenylalanine-free diet. If they are put on this diet right away and stay on it, these children avoid the severe effects of PKU. - A functional polymorphismPolymorphism (biology)Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
in the monoamine oxidase A (MAOA) geneMonoamine oxidaseL-Monoamine oxidases are a family of enzymes that catalyze the oxidation of monoamines. They are found bound to the outer membrane of mitochondria in most cell types in the body. The enzyme was originally discovered by Mary Bernheim in the liver and was named tyramine oxidase...
promoter can moderate the association between early life trauma and increased risk for violence and antisocial behaviorAntisocial personality disorderAntisocial personality disorder is described by the American Psychiatric Association's Diagnostic and Statistical Manual, fourth edition , as an Axis II personality disorder characterized by "...a pervasive pattern of disregard for, and violation of, the rights of others that begins in childhood...
. Low MAOA activity is a significant risk factorRisk factorIn epidemiology, a risk factor is a variable associated with an increased risk of disease or infection. Sometimes, determinant is also used, being a variable associated with either increased or decreased risk.-Correlation vs causation:...
for aggressive and antisocial behavior in adults who report victimization as children. Persons who were abused as children but have a genotype conferring high levels of MAOA expression are less likely to develop symptoms of antisocial behavior. These findings must be interpreted with caution, however, because gene association studies on complex traits are notorious for being very difficult to confirm.
Medical significance
- Doctors are interested in knowing whether disease can be prevented by reducing exposure to environmental risks. Gene–environment interaction means that some people carry genetic factors that confer susceptibility or resistance to a certain disorder in a particular environment. It has been argued that there may be significant public healthPublic healthPublic health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" . It is concerned with threats to health based on population health...
benefits in using genetic information to stratify the allocation of environmental interventions that prevent disease, although this viewpoint is not universally held.
- PharmacogeneticsPharmacogeneticsThe terms pharmacogenomics and pharmacogenetics tend to be used interchangeably, and a precise, consensus definition of either remains elusive...
is the study of genetic variationGenetic variationGenetic variation, variation in alleles of genes, occurs both within and among populations. Genetic variation is important because it provides the “raw material” for natural selection. Genetic variation is brought about by mutation, a change in a chemical structure of a gene. Polyploidy is an...
that causes people to respond differently to drugs. The clinical importance of pharmacogenetics comes from the possibility that drug treatment can be made safer and more effective when the patient's genotype is known. Pharmacogenetic studies can be considered studies of gene–environment interaction, with drug treatment as the environmental variable.
Timing of environmental effects
The popular description of an animal being "born that way" does not necessarily discriminate genetic from environmental effects. In viviparous animalsVivipary
Vivipary has two different meanings. In animals, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs...
, such as human
Human
Humans are the only living species in the Homo genus...
s, environmental influences may act during either pre- or post-natal development; similarly environmental influences may act before and after hatching to affect development in oviparous animals. Environmental influences in utero
In utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...
may be as strong and lasting as genetic or post-natal environmental influence. There is increasing study of environmental influences affecting genetic factors directly but nonheritably; see the Epigenetics
Epigenetics
In biology, and specifically genetics, epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence – hence the name epi- -genetics...
article for a detailed discussion.
See also
- Diathesis–stress model
- Epigenetic TheoryEpigenetic TheoryEpigenetic theory is an emergent theory of development that includes both the genetic origins of behavior and the direct influence that environmental forces have, over time, on the expression of those genes...
- Evolutionary developmental psychologyEvolutionary developmental psychologyEvolutionary developmental psychology, , is the application of the basic principles of Darwinian evolution, particularly natural selection, to explain contemporary human development...
- Differential SusceptibilityDifferential susceptibility hypothesisAccording to the differential susceptibility hypothesis by Belsky individuals vary in the degree they are affected by experiences or qualities of the environment they are exposed to...
- Biopsychosocial modelBiopsychosocial modelThe biopsychosocial model is a general model or approach that posits that biological, psychological , and social factors, all play a significant role in human functioning in the context of disease or illness...
- Gene-environment correlationGene-environment correlationGene-environment correlation is said to occur when exposure to environmental conditions depends on an individual's genotype.-Definition:...