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Although childhood and adult IQs are known to be correlated, the determinants of the correlation are not. To examine this issue, researchers sought genetic and environmental contributions to IQ among 1940 unrelated individuals from two Scottish birth cohorts.
Participants' IQs had been tested at mean age 11 and later in life, at age 65, 70, or 79. Phenotypic variation was defined as the difference between an individual's IQ at age 11 and in old age; genetic variation was defined as the difference across individuals' IQs. Genotyping of 536,295 autosomal single nucleotide polymorphisms (SNPs) was performed.
Causal variants transmitted with common SNPs (i.e., variants in linkage disequilibrium with SNPs) were considered to explain 0.24 of the ph…