The Fund seeks to track the investment results of the Bloomberg U.S. MBS Index (the Underlying Index), which measures the performance of investment-grade (as determined by Bloomberg Index Services Limited (the Index Provider or Bloomberg)) mortgage-backed pass-through securities (MBS) issued or guaranteed by U.S. government agencies or sponsored entities. The Underlying Index includes fixed-rate MBS issued by the Government National Mortgage Association (GNMA or Ginnie Mae), Federal National Mortgage Association (Fannie Mae) and Federal Home Loan Mortgage Corporation (Freddie Mac) that have 30-, 20-, or 15-year maturities. All securities in the Underlying Index must have a remaining weighted average maturity of at least one year. In addition, the securities in the Underlying Index must be denominated in U.S. dollars and must be non-convertible. The Underlying Index is market capitalization-weighted and the securities in the Underlying Index are updated on the last business day of each month.