Abstract: Generation and properties of dark solitons are studied in detail by means of numerical simulation of quasi one-dimensional heteronuclear two-component Bose-Einstein condensates in syntonic potential. Dark solitons are only induced in one of the condensate components by modulational instability with instantaneous conversion of repulsive interspecies interaction to attraction. Solitons pass through each other periodically in syntonie potential. In addition, the number of dark solitons is affiliated with ratio of particle mass and ratio of particles numbers.