Molecular Genetics Research on IQ: Can it be done?
It is clear from a range of studies of familial influences on IQ that a large number of genetic factors contribute to IQ. A common starting point for genetic analysis is linkage analysis within families. Since this requires an identifiable marker linked to the gene of interest, it can only be extended to whole populations if the genome is so densely mapped that very close markers indeed can be found. If recombination between gene of interest and marker is as little as 0.001 then linkage disequilibrium can persist for around 8000 years. This approach assumes that an apparently continuous trait such as intelligence can be the result of a finite number of discrete genes acting together. Diagram 1 shows how as few as 3 loci giving rise to 7 phenotypes produce continuous variation within the population. This model has been shown to be valid for a wide range of characteristics from the quantity of juice in tomatoes to glucose tolerance in mice. Should research into the molecular genetics of
