The investment seeks to track the investment results of the Bloomberg Barclays U.S. MBS Index. The fund seeks to track the performance of the underlying index by investing at least 90% of its assets in the securities of the underlying index and in investments that provide substantially similar exposure to securities in the underlying index. The index measures the performance of investment-grade mortgage-backed pass-through securities (MBS) issued or guaranteed by U.S. government agencies or sponsored entities.