What process powers the movement of tectonic plates? describe how this process works.

The tectonic plates move and shift due to Mantle convection

Mantle convection is caused by the magma in the mantle of the earth constantly being cooled near the crust and heated the closer it gets to the core and like normal convection the cool magma sinks towards the crust and the hot magma rises to the crust. this happens in a circular motion causing the crust to shift with the magma 

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.