We developed a computational model to simulate the growth of multicellular tissues using a discrete approach based on cellular automata. The model allows us to study the tissue growth rates and population dynamics of different populations of migrating and proliferating mammalian cells. Cell migration is modeled using a discrete-time Markov chain approach. We report simulation results describing cell collision and aggregation for two cell populations each having its own division and motion characteristics. Heterotypic and homotypic cell-cell interactions play important roles in cell and tissue functions. The temporal evolution of the frequency of cell collision and aggregation and their relations...