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DOF has nothing to do with MP.
To a first approximation, yes.
However, diffraction starts showing its effects on a 36 Mpix sensor at medium apertures (at f/13 for sure), thus reducing the perceived sharpness and, therefore, also DOF.
Diffraction has the effect to alter the circle of confusion, by transforming points and circles into circles and larger circles, respectively.
A good reading, here.