Normally at least 80% of the fund's assets are invested in mortgage-related securities, including securities collateralized by mortgage loans and contracts for future delivery of such securities (such as to be announced contracts and mortgage dollar rolls). The fund invests primarily in mortgage-related securities that are sponsored or guaranteed by the U.S. government, such as securities issued by government-sponsored entities that are not backed by the full faith and credit of the U.S. government, and non-government mortgage-related securities.