The output from two grating-stabilized external-cavity diode lasers were injected into a single-mode diode laser. Operating at a wavelength of $780\mathrm{nm}$ , this laser produced $\sim 50\mathrm{mW}$ of power with two main frequency components of the same spectral characteristics of the seed lasers. The power ratio of the amplified components was freely adjustable due to gain saturation, and amplification was observed for frequency differences of the two seed lasers in the range from $73\mathrm{MHz}$ to $6.6\mathrm{GHz}$ . This system was used to realize a dual isotope magneto-optic trap (MOT) for rubidium ( ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ ). The resulting position and cloud size of the dual isotope MOT was the same as that of the single species MOTs to within $\pm 10$ and $\pm 20\mathrm{\mu }\mathrm{m}$ , respectively. We also characterized the additional spectral components produced by four wave mixing (FWM) in the diode laser amplifier and utilized a particular FWM sideband to realize hyperfine pumping and subsequent laser trapping of ${}^{85}\mathrm{Rb}$ in the absence of a “repump” laser dedicated to hyperfine pumping.