Couples tend to be more similar in IQ than would occur by random mate choice (assortative mating) and this similarity is associated with an unknown correlation m of their genotypes." 

The genetic correlation is the degree of statistical association between genotypes of parents and children, which is 0.5 if the parents’genotypes are uncorrelated (random mating). But couples tend to be more similar in IQ thanwould occur by random mate choice (assortative mating) and this similarity is associated with an unknown correlation m of their genotypes. The effect is to raise the genetic correlation of parent and offspring to (1 + m)/2.

So m=0.2 means parents IQs are positively correlated at about 0.2. 

Thanks; I'm surprised m isn't higher.

If h=1 and m=1, intergenerational correlation of lifetime income would be only 0.07 in that formula.