[Genetics of development and behaviour].

Quantitative genetics can make a significant contribution to disentangle the relative influence of genetics and environment on human development and its disorders. Estimates of Pearson s correlation coefficients between siblings, mono and dizogotic twins reared together or apart, allows the calculation of heredability, that is, the contribution of genetics to the variance of a given trait. In the case of many aspects of intellectual development, heredability is around 50%. The rests is attributable to the influence of environment. The influence of genetics on development should be considered as a trend, a risk, rather than a programmed fate.