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== History ==
Estimation in biology/animal breeding using standard [[Analysis of variance|ANOVA]]/[[Restricted maximum likelihood|REML]] methods of variance components such as heritability, shared-environment, maternal effects etc. typically requires individuals of known relatedness such as parent/child; this is often unavailable or the pedigree data unreliable, leading to inability to apply the methods or requiring strict laboratory control of all breeding (which threatens the [[external validity]] of all estimates), and several authors have noted that relatedness could be measured directly from genetic markers (and if individuals were reasonably related, economically few markers would have to be obtained for statistical power), leading Kermit Ritland to propose in 1996 that directly measured pairwise relatedness could be compared to pairwise phenotype measurements (Ritland 1996, [http://www.genetics.forestry.ubc.ca/ritland/reprints/1996_Evolution_HeritInFieldModel.pdf "A Marker-based Method for Inferences About Quantitative Inheritance in Natural Populations"]<ref>see also Ritland 1996b, [http://genetics.forestry.ubc.ca/ritland/reprints/1996_GenetResearch_r.pdf "Estimators for pairwise relatedness and individual inbreeding coefficients"]; Ritland & Ritland 1996, [http://genetics.forestry.ubc.ca/ritland/reprints/1996_Evolution_HeritInFieldMimulus.pdf "Inferences about quantitative inheritance based on natural population structure in the yellow monkeyflower, ''Mimulus guttatus''"]; Lynch & Ritland 1999, [http://www.genetics.org/content/152/4/1753.full "Estimation of Pairwise Relatedness With Molecular Markers"]; Ritland 2000, [http://www.genetics.forestry.ubc.ca/RITLAND/reprints/2000_ME_Review.pdf "Marker-inferred relatedness as a tool for detecting heritability in nature"]; Thomas 2005, [https://www.dropbox.com/s/45kxuo2p00lii6k/2005-thomas.pdf "The estimation of genetic relationships using molecular markers and their efficiency in estimating heritability in natural populations"]</ref>).
As genome sequencing costs dropped steeply over the 2000s, acquiring enough markers on enough subjects for reliable estimates using very distantly related individuals became possible. An early application of the method to humans came with Visscher et al. 2006<ref>Visscher et al 2006, [http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.0020041 "Assumption-free estimation of heritability from genome-wide identity-by-descent sharing between full siblings"]</ref>/2007,<ref>Visscher et al 2007, [http://www.sciencedirect.com/science/article/pii/S0002929707638841 "Genome partitioning of genetic variation for height from 11,214 sibling pairs"]</ref> which used SNP markers to estimate the actual relatedness of siblings and estimate heritability from the direct genetics. In humans, unlike the original animal/plant applications, relatedness is usually known with high confidence in the 'wild population', and the benefit of GCTA is connected more to avoiding assumptions of classic behavioral genetics designs and verifying their results, and partitioning heritability by SNP class and chromosomes. The first use of GCTA proper in humans was published in 2010, finding 45% of variance in human height can be explained by the included SNPs.<ref name="Yang2010">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3232052/ "Common SNPs explain a large proportion of heritability for human height"], Yang et al 2010</ref><ref>[http://emilkirkegaard.dk/en/wp-content/uploads/A-Commentary-on-Common-SNPs-Explain-a-Large-Proportion-of-the-Heritability-for-Human-Height-by-Yang-et-al.-2010.pdf "A Commentary on ‘Common SNPs Explain a Large Proportion of the Heritability for Human Height’ by Yang et al. (2010)"], Visscher et al 2010</ref> (Large GWASes on height have since confirmed the estimate.<ref name="Wood2014">[http://neurogenetics.qimrberghofer.edu.au/papers/Wood2014NatGenet.pdf "Defining the role of common variation in the genomic and biological architecture of adult human height"], Wood et al 2014</ref>) The GCTA algorithm was then described and a software implementation published in 2011.<ref>[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3014363/ "GCTA: A Tool for Genome-wide Complex Trait Analysis"], Yang et al 2011</ref> It has since been used to study a wide variety of biological, medical, psychiatric, and psychological traits in humans, and inspired many variant approaches.
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