Genome-wide complex trait analysis: Difference between revisions

Revision as of 19:51, 14 January 2019

Revision as of 16:28, 31 January 2019

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{{main|Twin study#Criticism}}

Twin and family studies have long been used to estimate variance explained by particular categories of genetic and environmental causes. Across a wide variety of human traits studied, there is typically minimal shared-environment influence, considerable non-shared environment influence, and a large genetic component (mostly additive), which is on average ~50% and sometimes much higher for some traits such as height or intelligence.<ref>[http://www.gwern.net/docs/genetics/2015-polderman.pdf "Meta-analysis of the heritability of human traits based on fifty years of twin studies"], Polderman et al 2015</ref> However, the twin and family studies have been criticized for their reliance on a number of assumptions that are difficult or impossible to verify, such as the equal environments assumption (that the environments of [[monozygotic]] and [[dizygotic]] twins are equally similar), that there is no misclassification of zygosity (mistaking identical for fraternal & vice versa), that twins are unrepresentative of the general population, and that there is no [[assortative mating]]. Violations of these assumptions can result in both upwards and downwards bias of the parameter estimates.<ref>{{Cite journal|last=Barnes|first=J. C.|last2=Wright|first2=John Paul|last3=Boutwell|first3=Brian B.|last4=Schwartz|first4=Joseph A.|last5=Connolly|first5=Eric J.|last6=Nedelec|first6=Joseph L.|last7=Beaver|first7=Kevin M.|date=2014-11-01|title=Demonstrating the Validity of Twin Research in Criminology|url=https://www.researchgate.net/profile/Brian_Boutwell/publication/267158254_Demonstrating_the_validity_of_twin_research_in_criminology/links/545d24af0cf27487b44d4ae3.pdf267158254|journal=Criminology|language=en|volume=52|issue=4|pages=588–626|doi=10.1111/1745-9125.12049|issn=1745-9125}}</ref> (This debate & criticism have particularly focused on the [[heritability of IQ]].)

The use of SNP or whole-genome data from unrelated subject participants (with participants too related, typically >0.025 or ~fourth cousins levels of similarity, being removed, and several [[Principal component analysis|principal components]] included in the regression to avoid & control for [[population stratification]]) bypasses many heritability criticisms: twins are often entirely uninvolved, there are no questions of equal treatment, relatedness is estimated precisely, and the samples are drawn from a broad variety of subjects.