Apparatus is disclosed for controlling the heating and cooling of a plurality of upright containers containing a mixture used for performing gene amplification. The apparatus includes a support rack comprising aluminum blocks which is partially submerged in a thermally conductive fluid such that at least the lower portions of the containers are submerged in the fluid with the upper portions engaging the aluminum blocks for efficient heat transfer. Heaters are disposed within the aluminum block for heating the block and a plurality of thermoelectric cooling cells are used to cool the block. A programmable microprocessor is used for controlling the heating and cooling cycles, thereby allowing repetitive heating and cooling of the mixture to produce the copies of the genetic material sought to be copied. A cam separates the support rack from the cooling cells during the heating portion of the process.