A new look at the challenging world of tandem repeats

Recent research has shown a correlation between some genetic diseases and g enomic sequences tandemly repeated a variable and excessive number of times . The excessive number of tandem repeats is usually caused by a progressive expansion, generally considered as purely harmful. We put forward a number of hypotheses: the main one is that the number of repeats has normally a s pecific significance, and that there exist purposive mechanisms having as a primary function the management of tandem repeats length; such a function is generally useful and only rarely may it become harmful, because of some malfunctioning. These hypotheses are suggested by plausibility arguments, a nd are supported by a number of recent experimental results. They could pro vide a simple and unifying explanation of many pathological and non-patholo gical phenomena replacing many ad hoc assumptions. We finally propose to ca ll the study of the above tandem repeat managing mechanisms 'dynamical gene tics'. (C) 2000 Harcourt Publishers Ltd.