Genetic association
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Genetic association is when one or more
Studies of genetic association aim to test whether single-locus
Description
Genetic association can be between phenotypes, such as visible characteristics such as flower color or height, between a phenotype and a genetic polymorphism, such as a
Linkage disequilibrium (LD) is a term used in the study of population genetics for the non-random association of alleles at two or more loci, not necessarily on the same chromosome. It is not the same as linkage, which is the phenomenon whereby two or more loci on a chromosome have reduced recombination between them because of their physical proximity to each other. LD describes a situation in which some combinations of alleles or genetic markers occur more or less frequently in a population than would be expected from a random formation of haplotypes from alleles based on their frequencies.[citation needed]
Genetic association studies are performed to determine whether a genetic variant is associated with a disease or trait: if association is present, a particular allele, genotype or haplotype of a polymorphism or polymorphisms will be seen more often than expected by chance in an individual carrying the trait. Thus, a person carrying one or two copies of a high-risk variant is at increased risk of developing the associated disease or having the associated trait.[citation needed]
Studies
Case-control designs
One problem with the case-control design is that genotype and haplotype frequencies vary between ethnic or geographic populations. If the case and control populations are not well matched for ethnicity or geographic origin then false positive association can occur because of the confounding effects of
Family based designs
Family based association designs aim to avoid the potential confounding effects of population stratification by using the parents or unaffected siblings as controls for the case (the affected offspring/sibling). Two similar tests are most commonly used, the
Quantitative trait association
A quantitative trait (see quantitative trait locus) is a measurable trait that shows continuous variation, such as height or weight. Quantitative traits often have a 'normal' distribution in the population. In addition to the case control design, quantitative trait association can also be performed using an unrelated population sample or family trios in which the quantitative trait is measured in the offspring.
Evidence
Evidence of the association is based on MNAs that are usually based on studies that include large sample sizes like genome-wide association studies. With only little empirical data associating study results and study design, bias in genetic association studies are not well understood.[2]
Reporting outcomes
Based on traits either continuous or binary, heritability (going from 0 to 1 with 0 meaning non-hertiable) outcomes are usually reported respectively by the proportion of phenotypic variation that can be attributed to genetic variation or the proportion of variance attributed to genetic variation.[3]
See also
- Disease gene identification
- Association mapping
- Family based QTL mapping
- Genetic epidemiology
- Genetic linkage
- Genome-wide association study
- Linkage disequilibrium
- Personality genetics
References
External links
- A list of computer programs for genetic analysis including genetic association analysis
- GWAS Central – a central database of summary-level genetic association findings.