Extending the definition of additive genetic variance to more than one gene- a viewpoint

Following the Fisherian approach, the expression for additive genetic variance is derived in a single gene system through a regression equation in two variables which are used to obtain the additive and dominance variances. The approach is extended to two genes with restricted linkage and inbreeding. It was brought out that additive genetic variance defined essentially for one gene does not extendper se to multi-gene systems