Whenever a vacancy exists in any position in the service of the city, it shall be filled by appointment of a person on the appropriate eligible register of the board. The vacancy may be filled from the eligible qualified applicants which are on the appropriate register, or by transfer within the service of the city from another position of essentially the same class. However, the ranking layoff of the same class shall be appointed in every instance. The appointing authority may reject any eligible list and the list shall be abolished. The governing body may fill a vacancy temporarily pending the establishment of an eligible register. No authorization may be given for longer than 120 calendar days, and no employee shall have status under this part. All appointments, other than temporary appointments, shall be probationary for 12 months from the date of the appointment. A probationary subordinate employee may be discharged by the appointing authority for unsatisfactory service at any time before the expiration of that period if the action is approved by the governing body. A probationary department head may be discharged or demoted similarly by the governing body. The discharge of a probationary employee shall be reported to the board at the next regularly scheduled meeting of the board held after the discharge. After the expiration of the probationary period, an appointment shall become permanent.