Tenn. Code Ann. § 71-1-106

The chief administrative and executive officer of the department shall be appointed by the governor solely on a basis of merit as measured by education, ability, and experience in the administration of public welfare activities and without regard to residence or political affiliation. Such officer shall serve at the pleasure of the governor. Such officer shall have general charge and supervision of the department and shall appoint the heads of such divisions as may be created. The choice of personnel shall be made on the basis of merit as measured by experience and training in each particular field. Vacancies in superior positions shall be filled so far as practicable by promotion based on meritorious service.