The effect of a fusion of subpopulations on the total fixation index.

A general mathematical expression is found for the decrease in the fixation index of a population where subpopulations with different gene frequencies fuse. It is shown that the use of Wright's formulas for a hierarchic structure will not necessarily give the correct result in this situation, since the conditions for their application are usually not satisfied. Two examples are given, one with fusions among subpopulations with a continuously distributed gene frequency, and one with data from real observations producing a discrete distribution.