When parental populations give rise to a hybrid population, it is possible to estimate the proportions of admixture from each parental population on the basis of known marker allele frequencies if there has been no genetic drift. Methods include generalized least squares and maximum likelihood. It is also possible to use a measure of genetic similarity. All these methods assume that the admixture is a static, one-time phenomenon, whereas in reality there is usually a continued, long-term exchange of genes among populations.