In this paper we investigate derivations of a commutative powerassociative algebra. Particular cases of stable and partially stable algebras are inspected. Some attention is paid to the Jordan case. Further results are given. Especially, we show that the core of an th-order Bernstein algebra which is power-associative is a Jordan algebra. 1. Preliminaries. Weighted algebras are non-associative algebras modeling concrete biological situations. Their origin lies in the work of IMH Etherington (see [4]) who gave a mathematical formulation of the Mendelian laws in the language of algebras. Since then, many authors have contributed to the study of these algebras from various points of view, and there is at present a substantial bibliography on the subject. In a recent survey [18] a general introduction to algebras arising in genetics can be found. Different classes of weighted …