Concordance (genetics)
Encyclopedia
Concordance as used in genetics
usually means the presence of the same trait in both members of a pair of twins
. However, the strict definition is the probability that a pair of individuals will both have a certain characteristic, given that one of the pair has the characteristic. For example, twins are concordant when both have or both lack a given trait. Ideally, concordance includes that of identical twins.
compares the concordance rate of identical twins to that of fraternal twins. This can help determine whether the disease has a genetic cause. Controversial uses of twin data have looked at concordance rates for homosexuality
and intelligence.
Because identical twins are genetically identical, it follows that any genetic mutation carried by one would also be carried by the other. If a characteristic identified in one twin is caused by a genetic mutation, then it should also be present in the other twin. Thus, the concordance rate of a given characteristic helps establish whether or to what extent it is caused by genetic mutation.
There are several problems with this assumption:
studies where DNA is directly assayed for positions of variance (see SNP
), concordance is a measure of the percentage of SNPs
that are measured as identical. Samples from the same individual or identical twins theoretically have a concordance of 100%, but due to assaying errors and somatic mutations, they are usually found in the range of 99% to 99.95%. Concordance can therefore be used as a method of assessing the accuracy of a genotyping
assay
platform.
Because a child inherits half of its DNA
from each parent, parents and children, siblings, and fraternal (dizygotic) twins have a concordance around 50% using this measure.
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
usually means the presence of the same trait in both members of a pair of twins
TWINS
Two Wide-Angle Imaging Neutral-Atom Spectrometers are a pair of NASA instruments aboard two United States National Reconnaissance Office satellites in Molniya orbits. TWINS was designed to provide stereo images of the Earth's ring current. The first instrument, TWINS-1, was launched aboard USA-184...
. However, the strict definition is the probability that a pair of individuals will both have a certain characteristic, given that one of the pair has the characteristic. For example, twins are concordant when both have or both lack a given trait. Ideally, concordance includes that of identical twins.
Twin studies
A twin studyTwin study
Twin studies help disentangle the relative importance of environmental and genetic influences on individual traits and behaviors. Twin research is considered a key tool in behavioral genetics and related fields...
compares the concordance rate of identical twins to that of fraternal twins. This can help determine whether the disease has a genetic cause. Controversial uses of twin data have looked at concordance rates for homosexuality
Homosexuality
Homosexuality is romantic or sexual attraction or behavior between members of the same sex or gender. As a sexual orientation, homosexuality refers to "an enduring pattern of or disposition to experience sexual, affectional, or romantic attractions" primarily or exclusively to people of the same...
and intelligence.
Because identical twins are genetically identical, it follows that any genetic mutation carried by one would also be carried by the other. If a characteristic identified in one twin is caused by a genetic mutation, then it should also be present in the other twin. Thus, the concordance rate of a given characteristic helps establish whether or to what extent it is caused by genetic mutation.
There are several problems with this assumption:
- A given genetic mutation may not have 100% penetrancePenetrancePenetrance in genetics is the proportion of individuals carrying a particular variant of a gene that also express an associated trait . In medical genetics, the penetrance of a disease-causing mutation is the proportion of individuals with the mutation who exhibit clinical symptoms...
, in which case it may have different phenotypicPhenotypeA phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
consequences in genetically identical individuals; - Developmental and environmental conditions may be different for genetically identical individuals. If developmental and environmental conditions contribute to the development of the disease or other characteristic (as is almost always the case), there can be differences in the outcome of genetically identical individuals;
- The logic is further complicated if the characteristic is polygenic, i.e. caused by mutations in more than one gene.
- epigenetic effects can alter the genetic expressions in twins through varied exposure of chemicals, dietary habits and environmental factors. The epigenetic effect is least when young and increases with age, as the identical twins grow older.http://www.bio-medicine.org/medicine-news/Inherent-similarities-in-identical-twins-may-not-be-so-strong-3891-1/
- Where in the absence of one or more environmental factors a condition will not develop in an individual, even with high concordance rates, the proximate cause is environmental, with strong genetic influence: thus "a substantial role of genetic factors does not preclude the possibility that the development of the disease can be modified by environmental intervention." http://pediatrics.aappublications.org/cgi/content/full/121/3/493 so "genetic factors are assumed to contribute to the development of that disease." but cannot be assumed alone to be causal http://pediatrics.aappublications.org/cgi/content/full/121/3/493
Genotyping studies
In genotypingGenotyping
Genotyping is the process of determining differences in the genetic make-up of an individual by examining the individual's DNA sequence using biological assays and comparing it to another individual's sequence or a reference sequence. It reveals the alleles an individual has inherited from their...
studies where DNA is directly assayed for positions of variance (see SNP
Single nucleotide polymorphism
A single-nucleotide polymorphism is a DNA sequence variation occurring when a single nucleotide — A, T, C or G — in the genome differs between members of a biological species or paired chromosomes in an individual...
), concordance is a measure of the percentage of SNPs
Single nucleotide polymorphism
A single-nucleotide polymorphism is a DNA sequence variation occurring when a single nucleotide — A, T, C or G — in the genome differs between members of a biological species or paired chromosomes in an individual...
that are measured as identical. Samples from the same individual or identical twins theoretically have a concordance of 100%, but due to assaying errors and somatic mutations, they are usually found in the range of 99% to 99.95%. Concordance can therefore be used as a method of assessing the accuracy of a genotyping
Genotyping
Genotyping is the process of determining differences in the genetic make-up of an individual by examining the individual's DNA sequence using biological assays and comparing it to another individual's sequence or a reference sequence. It reveals the alleles an individual has inherited from their...
assay
Assay
An assay is a procedure in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample. A quantitative assay may also measure the amount of a substance in a sample. Bioassays and immunoassays are among the many varieties of specialized...
platform.
Because a child inherits half of its DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
from each parent, parents and children, siblings, and fraternal (dizygotic) twins have a concordance around 50% using this measure.