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In genetics, association mapping, also known as "linkage disequilibrium mapping", is a method of mapping quantitative trait loci (QTLs) that takes advantage of historic linkage disequilibrium to link phenotypes (observable characteristics) to genotypes (the genetic constitution of organisms), uncovering genetic associations.
Once linkage disequilibrium has been calculated for a dataset, a visualization method is often chosen to display the linkage disequilibrium to make it more easily understandable. The most common method is to use a heatmap, where colors are used to indicate the loci with positive linkage disequilibrium, and linkage equilibrium. This example ...
The approach involves using regression analysis to examine the relationship between linkage disequilibrium scores and the test statistics of the single-nucleotide polymorphisms (SNPs) from the GWAS. Here, the "linkage disequilibrium score" for a SNP "is the sum of LD r 2 measured with all other SNPs". [3]
Hence, GWAS is a non-candidate-driven approach, in contrast to gene-specific candidate-driven studies. GWA studies identify SNPs and other variants in DNA associated with a disease, but they cannot on their own specify which genes are causal. [1] [2] [3] The first successful GWAS published in 2002 studied myocardial infarction. [4]
By observing if frequencies of a specific variant are more commonly associated, or higher than expected, with the given trait; an association is developed between the trait and the variant. However, many of these associations can be developed throughout an individual due to linkage disequilibrium and the large size of the genome. Although GWAS ...
The most commonly used approach, block-based method, exploits the principle of linkage disequilibrium observed within haplotype blocks. [12] Several algorithms have been devised to partition chromosomal regions into haplotype blocks which are based on haplotype diversity , LD , four-gamete test and information complexity and tag SNPs are ...
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 ...
(Using a Plomin example, [38] for two traits with heritabilities of 0.60 & 0.23, =, and phenotypic correlation of r=0.45 the bivariate heritability would be =, so of the observed phenotypic correlation, 0.28/0.45 = 62% of it is due to correlative genetic effects, which is to say nothing of trait mutability in and of itself.)