The 12 C(␥ ជ ,pp) and 12 C(␥ ជ ,pn) reactions have been studied for E ␥ ϭ160Ϫ350 MeV using linearly polarized photons from the Glasgow tagged photon spectrometer at the Mainz microtron MAMI. Both reaction channels show a negative photon asymmetry ⌺ for missing energies E m below 70 MeV, where direct emission nucleon pairs is expected. A strong peak at low E m is observed in ⌺ (␥,pp) , but not in ⌺ (␥,pn) . Further differences between the two reaction channels are observed in the E ␥ dependence of ⌺ and in the angular distributions of differential cross sections for photons polarized parallel, or perpendicular, to the reaction plane. Theoretical calculations using an unfactorized distorted wave treatment of direct two-nucleon emission do not agree with the magnitude of the photon asymmetry or the angular dependence of the differential cross sections for either channel. For E m Ͼ70 MeV and E ␥ Ͼ250 MeV, ⌺ has a substantial negative value which is similar for both reaction channels. This is attributed to two-step reactions following initial quasifree pion production.