Polymorphisms at tandem repeat loci are caused by mutations with allele sizes occasionally altered by more than one repeat unit in both forward and backward directions. Such mutational changes may occur with asymmetric probabilities. Therefore, a one-step symmetric stepwise mutation model may not be appropriatefor studying the population dynamics at all repeat loci. In this work, we evaluatedthe expectation and variance of the within-population variance of the allele sizedistribution in a finite population, and the expected homozygosity at a locus by thecoalescence approach under a general stepwise mutation model, where mutationaltransitions of allele sizes can be arbitrary, including being asymmetric.