The present study investigates the effect that different patterns of migration have on the genetic structure of source-sink metapopulations specifically modelling the dynamics of local populations. The model assumes a metapopulation consisting of a single source and s different sink populations and considers the expected number of nucleotide differences between two genes drawn at random from the source-sink metapopulation. The results show that a collection of interconnected sinks can maintain a substantial fraction of the genetic variability observed in the source population, particularly where migration from the source is continuous over time. The degree of genetic differentiation among the sinks might be large, especially if migration from the source is stochastic. Genetic differentiation is small when extinctions are frequent (because most of the sink populations are composed of recent migrants from the source) or extremely rare (because of the increased effect of migration among sinks), being maximized when the frequency of extinctions is between these two extremes.