risk allele individual harbours relative individual harbour risk allele ref name bland ref described math r math metric effects individual genetic variants ''complex'' human behavioural traits disorders vanishingly small variant accounting math r math variation phenotype ref name mcguegottesman fact discovered primarily genome wide association studies complex behavioural phenotypes including results substance use ref name thorgeirssongudbjartsson ref name schumanncoin personality ref name okbaybaselmans fertility ref name dayhelgason ref schizophrenia ref name swg depression ref name okbaybaselmans ref name caibigdeli ref endophenotypes including brain structure ref name hibarstein function ref name iaconovaidyanathan ref
Natural science Biology Genetics Behavioural genetics