The investment seeks to track the investment results of the Bloomberg Barclays U.S. GNMA Bond Index. The fund generally will invest at least 90% of its assets in the component securities of the underlying index and in investments that have economic characteristics that are substantially identical to the component securities of the underlying index. The underlying index includes fixed-rate MBS issued by GNMA that have 30- or 15-year maturities. The index measures the performance of mortgage-backed pass-through securities issued by GNMA.