Interaction of Heritability & Environment

Variation can be quantified

       mean  standard deviation: 
       variance: 2

Variation has two sources: genetic (G2) & environmental (E2) variance

      phenotypic variance      P2  = G2 + E2 + GxE2
      additive variance            A2  = G2 + E2 
      heritability                        h2  = G2/A2  = G2 / (G2 + E2)

          "Heritability in the narrow sense" ignores interaction variance ( GxE2)
           Identical genotypes produce different phenotypes in different environments.

           Ex.: Hypothetical IQ scores change according to adoptive environment

IQ correlation analysis

Mean IQ score of Children is 20 pts higher than midpoint of Biological Parents;
     Each child's IQ score has been raised by modified adoptive environment.
     IQ scores of Biological Parents and their Children remain perfectly correlated (BxC): h2 = 1.0

Mean IQ score of Children is identical to that of Adoptive Parents (115)
    AND scores of Children and Adoptive parents are uncorrelated: h2 < 0.1
            (  8  +   2  -   4  +   4  -   6  -   4 )  =     0 / 6 =  0

HOMEWORK: Is it possible that Adoptive parents choose Biological Parents with similar IQ?
                           Calculate the correlation between the Biological and Adoptive Parents (BxA)

All text material © 2014 by Steven M. Carr