HUMAN BEHAVIORAL-GENETICS OF COGNITIVE-ABILITIES AND DISABILITIES

Although neither the genome nor the environment can be manipulated in research on human behaviour, some of the new tools of molecular geneti cs can be brought to bear on human behavioural disorders (e.g. cogniti ve disabilities) and quantitative traits (e.g. cognitive abilities). T he inability to manipulate the human genome experimentally has had the positive effect of focusing attention on naturally occuring genetic v ariation responsible for behavioural differences among individuals in all their complex multifactorial splendour. Genes in such complex mult iple-gene systems are called quantitative trait loci (QTLs), which mer ge the two worlds of genetic research, quantitative genetics and molec ular genetics. Although most genetic research on complex human behavio ur has focused on severe mental disorders, cognitive abilities and dis abilities may be even more immediately relevant to neuroscience. For e xample, verbal ability and spatial ability are two of the most heritab le cognitive abilities, and reading disability is the first behavioura l disability for which replicated QTL linkage has been found. The purp ose of this essay is to provide an overview of the genetics of cogniti ve abilities and disabilities as an example of the impending merger of quantitative genetics and molecular genetics in QTL analysis of compl ex traits.