The board shall establish in the trust an individual investment account for each participant in the plan. All contributions by a participant or an employer for or on behalf of a participant shall be credited to the participant's individual investment account, together with all interest and investment earnings and losses. Investment and administrative fees, costs and expenses shall be charged to the participants' individual investment accounts except as otherwise provided under this part or as the General Assembly otherwise provides by appropriations from the General Fund. Employer defined contributions shall be recorded and accounted for separately from participant contributions, but all interest, investment earnings and losses, and investment and administrative fees, costs and expenses charged against individual investment accounts shall be allocated proportionately.